The taxa described under this family are Haploceras Zittel, 1870 and Hildoglochiceras Spath, 1924. The shell of Haploceras shows fine growth lines when epigenized shell is preserved, while inner casts are smooth, with a small but variable umbilicus that initially opens gradually until the last ontogenic stage when it slightly unfolds. Macroconchiate Haploceras show a slightly flexuous peristome, while assumed microconchs are variable in size, incorporate wide and short lappets rather than narrow and pedunculated ones, but can resemble glochiceratins in the absence of peristomal structures. Incomplete specimens of Haploceras make species-level interpretations difficult.

Reports of the genus Haploceras have been variably interpreted before the mid-twentieth century when this genus was commonly applied to Kimmeridgian and Lower Tithonian glochiceratins elsewhere in the world (e.g., Ziegler 1958), while the present knowledge about microconchiates is inconclusive. Across the Trans-Erythraean Trough, Haploceras has been more frequently reported from the northern and eastern margins than from western ones, although it is a rare genus across the Himalayas (from Uhlig 1903 to Énay 2009). Southwards across eastern margins, Haploceras has been reported from southern Pakistan to Madagascar throughout the twentieth century (e.g., Lemoine 1910; Collignon 1960; Fatmi and Zeiss 1994). In contrast, across western margins, Haploceras was only registered from southern Yemen (Howarth and Morris 1998) and Tanzania (from Zwierczyki 1914 to Bussert et al. 2009), being absent or very rare in between.

Haploceras elimatum (Oppel, 1965) and allies represent the morphological group more widespread and have been commonly reported throughout epicontinental areas in the Trans-Erythraean Trough. Haploceras elimatum (Oppel, 1965) and Haploceras staszycii (Zeuschner, 1846) have commonly been recognized as close species, difficult to separate, for instance by Rod (1937) and by (Hölder and Ziegler 1959), even as representing a single species (Rod 1946). They represent a dimorphic pair (Barthel 1962). The macroconch embraces all but one Tithonian haploceratin species with polymorphic microconchs (Énay and Cecca 1986). According to the information available, the latter is a rather speculative proposal. Zeiss (2001) highlighted the existing options for interpreting dimorphism in haploceratins, and treated the morphologically close species elimatum and staszycii as separate units only for convenience. Based on all the above mentioned, these two morphospecies are here interpreted as conspecific and referred to as Haploceras staszycii by priority, with reference to the closest nominal morphological species reported from the Trans-Erythraean Trough.

Hildoglochiceras is commonly more evolute, characterized by a median lateral groove and, consequently, with an acute-oval to oval whorl-section, venter of variable width and height, a lateral sulcus above the lower one-third of the flanks, a variable shell-size for the beginning of ribbing, and more or less ornamented outer whorls. In the present collection, we recognise two groups within Hildoglochiceras; one interpreted as microconch and other as the corresponding macroconch. These two morphs have been separated on the basis of shell size and the diameter of the umbilicus. The macroconch shows a subrectangular to oval whorl section. See previous chapters for a revision of reports of Hildoglochiceras across the Trans-Erythraean Trough.

Another comparable genus to inner whorls of Haploceras and Hildoglochiceras is Glochiceras Hyatt, 1900, the shell of which is smaller and shows a variable whorl section, sculpture and peristomal structure. The umbilicus of Glochiceras opens suddenly at the end of the growth. In addition, some species of Glochiceras are also characterised by a median lateral groove like in Hildoglochiceras. But small size, a rather discoid shell with narrow venter, the type of peristome, and the biostratigraphic range of typical Glochiceras, i.e. from Oxfordian to Kimmeridgian, with scarce records from the Lower Tithonian (e.g., Ziegler 1958; Collignon 1960; Barthel 1962; Grigore 2019), may be diagnostic. These morphological features persist in the scarce Glochiceras reported from the lowermost Tithonian of Europe. Separation of glochiceratins and microconchite haploceratins can be difficult with incomplete specimens lacking the peristome.

Among evolute haploceratins with a comparatively wide ventral region, Lingulaticeras Ziegler, 1958 and Paralingulaticeras Ziegler, 1958 are relatively close in shell-type to Hildoglochiceras. Supposed lowermost Tithonian forms of the former are more involute and show a sculptured venter of variable width, while those of the latter develop a latero-ventral tuberculation.

Ammonites elimatus (Oppel in Zittel 1868; SD Spath 1923); Tithonian.

Seven specimens, Hildoglochiceras Bed of Jara Dome (Lower Tithonian); KSKV2019Jara/61, 62, 63, 64, 66 (all figured), 68, 69 (figured).

Shell incomplete, compressed, involute with oval whorl section, moderately distinct to distinct umbilical shoulder, short and slightly arched umbilical wall. Maximum thickness of the shell is either at mid-lateral height or slightly below it. Height and thickness ratios with respect to diameter show variation. Suture lines preserved, densely frilled with most pronounced second lateral saddle, appears getting crowded anteriorly.

The specimens represent only parts of phragmocones and show erosional external surfaces. The ornamentation is not preserved in the present specimens. They appear smooth, as is typical for inner casts. However, parts of the siphuncle are well preserved. In two of the specimens (KSKV2019Jara/63 and 64) small portions of shell are preserved, also indicating a smooth external surface. The largest specimen (KSKV2019Jara/61) measured in the present collection has a diameter of ca. 53 mm and the crowding of the last septa indicates that it has attained the adult size. At a given diameter, the diameter of umbilicus may be larger but in general, the morphological features such as the shape of the shell, whorl section, suture lines and dimensional proportions match Haploceras elimatum (Oppel) (Collignon 1960: pl. 142, figs 536, 537) recorded from the Hildoglochiceras kobelli Zone of Madagascar (Early Tithonian) with a shell and ventral region clearly wider than in Oppel’s (1868) type. West-Tethyan Haploceras elimatum (Oppel) show more convergent, less inflated flanks, hence their “clear” separation from Haploceras staszycii (Zeuschner). Zeuschner (1846, pl. 4, fig. 3) did not give a scale with his figure. Zittel (1868: 81) mentioned a close morphologic similarity between H. elimatum of Oppel and H. staszycii of Zeuschner and stated that the specimen illustrated in Zeuschner (1846) is rather large (Zittel 1868: “ein ziemlich grosses Exemplar”) showing a smaller umbilicus and a wider shell than H. elimatum. Zittel’s (1870) description of H. staszycii (Zeuschner) was based on 300 specimens gathered from Rogoznik, Maruszina, central Apennines, and Bavaria. Zittel highlighted the shell-width and flattened flanks as distinguishing features to separate H. staszycii (Zeuschner) from H. elimatum (Oppel), although, he found difficulty in separating the young specimens of the two species. Zittel also made a rather uncommon observation about the occurrence of a keel-like elevation on the venter in the inner whorls up to 30 mm in shell size, but no further author mentioned this feature. If all the dimensional proportions of the specimens of H. staszycii (Zeuschner) and H. elimatum (Oppel), which are available (see Table 1) together with those of Zeuschner’s collection (300 specimens), croweding of septa in the largest phragmocone in the present collection and the figures of both the species illustrated by earlier workers are reviewed, there is a good possibility that H. staszycii (Zeuschner) represents the microconch whereas H. elimatum (Oppel) represents the marcoconch of the same species.

Haploceras subelimatum Fontannes (Collignon 1960: fig. 538) differs from Haploceras elimatum (Oppel) (Collignon 1960: pl. 142, figs 536, 537) in having a finer ornamentation, while the type of subelimatum in Fontannes (1879: 12, pl. 2, figs 5–6) shows a more compressed shell, and a general glochiceratin-like aspect. However, dimensional proportions are within the range of variation as seen in the specimens of the present collection (Fig. 7, also see table of dimensions). In the Stramberger specimen described by Oppel (1865: 549), the body chamber including the peristome is preserved. It measures 125 mm in diameter. The shell is either smooth or covered with fine curved growth lines.

Haploceras deplanatum Waagen (1875: 44, pl. 11, fig. 9a, b; Collignon 1960: pl. 142, figs 540–542) shows a similar H/T ratio (1.33–1.75) and U/D ratio (17–22) to the present specimens, however, Waagen’s specimen (1875) shows a more flattened shell, while the specimen of Madagascar (Collignon 1960, pl. 142, fig. 542) has a thicker whorl section at the corresponding diameters. If all the specimens described by Waagen and Collignon belong to the same species, then apparently there is a large range of variation in the H/T ratio (Fig. 7). In fact, later authors denied a conspecifity, and raised doubts about the interpretation of the Waagen type as Haploceras or Glochiceras given the absence of the peristome (e.g., Ziegler 1958). Waagen (1875) mentioned that the umbilical edge is not distinct. In contrast to his description which includes arched lateral surfaces and a steep slope of the umbilical wall. In the present specimens, the umbilical shoulder is moderately distinct, like in the specimens from Madagascar.

Furthermore, Collignon (1960: pl. 142, figs 540–542) assigned H. deplanatum to Glochiceras, because of their small size, but in the specimens figured by Collignon, there is no indication of a lateral groove and opening of the shell, which should have been visible at that diameter. In fact, his specimens are incomplete. Secondly, Glochiceras s. str. ranges from the Oxfordian to Kimmeridgian (Arkell et al. 1957: L274), but a single specimen was reported from the Lower Tithonian in Neuburg (Barthel 1962), and the records of Glochiceras reported by Collignon (1960) from the assumed Early Tithonian Hildoglochiceras kobelli Zone of Madagascar need confirmation.

Haploceras staszycii (Zeuschner) is a long-ranging species from the Upper Kimmeridgian to Tithonian and Lower Berriasian horizons elsewhere. The available data across the northern and eastern margins of the Trans-Erythraean Trough, indicate that Haploceras s.str. is a rare genus from the Spiti Shales. Spath (1928) assumed that Uhlig (1903) reported only a single example of Haploceras s. str., which is correct in the case of Haploceras indicum Uhlig, 1903 (coll. Diener, middle division of the Spiti Shales in Chojan), a form morphologically close to the Tithonian type of Haploceras staszycii (Zeuschner), or a local variant of this taxon. Yin and Énay (2004) reported and illustrated Haploceras sp. from a Lower Tithonian Uhligites-Aulacosphinctoides Assemblage in the Tibetan Himalayas, and envisaged that it resembles H. caractheis Zeuschner, the nominal species of reference for Énay and Cecca (1986). However, this cannot be evaluated from the illustration provided by Yin and Énay, while the occurrence of Haploceras from the Tibetan Himalayas was not confirmed by Énay (2009).

In southern Pakistan, Fatmi and Zeiss (1994) reported (without illustration) Haploceras cf. elimatum (Oppel) and Haploceras sp. from Upper Tithonian strata from the Chakkary/Draber and Phai sections, together with himalayitins or even above, in their “third fossil horizon” that may include some reworked ammonites. From Jaisalmer, Pandey and Krishna (2002) reported upper Lower Tithonian Haploceras together with Hildoglochiceras from their Communis Zone, and Krishna (2017) used records of the long-ranging genus Haploceras from Jaisalmer and Pakistan to interpret a mid-Early Tithonian age for the Natricoides Zone.

Waagen (1875) reported some species of Haploceras from Kachchh, but used this genus in a broader sense than it is used today, and applying it to forms from horizons most probably older than those typical for this genus. His Haploceras deplanatum does not belong to this genus, and his Haploceras propinquum collected from the lowest beds of the Katrol Group (= Jhuran Formation) “immediately above the oolite with Asp. perarmatum”, on the south side of Keera Hill near Charee, could refer to his Middle Kimmeridgian (i.e. to the Eudoxus-Steraspis stratigraphic interval according to Spath 1933) hence pointing to an extended lower range for Haploceras into the Kimmeridgian or, alternatively, to a large local stratigraphic gap if the taxonomic reinterpretation made by Spath (1928) applies. However, this latter interpretation at the genus level, recently assumed by Énay (2009), raises the need for a revision of the morphologic features typical of Haploceras. Spath (1924) recognized one example of Haploceras (= Glochiceras?) in the Blake collection, but no examples of Haploceras deplanatum Lemoine (non Waagen ?) sp. (= Glochiceras cf. Spath, 1928), which were commonly reported from Madagascar. Further Spath (1927: 6) identified abundant specimens of Haploceras elimatum (Oppel) included in an assemblage with belemnitids in the Andranosamonta Marls. He explained the scarcity of Haploceras in Kachchh due to the commonly occurring discontinuous sedimentary succession (Spath 1924, 1927). Nevertheless, there is a record of a Haploceras and Virgatosphinctes association within the Umia Group (= Jhuran Formation) (compare Spath 1927: 14). Spath (1928) reinterpreted the species Haploceras deplanatum Waagen with a lateral groove of variable depth as Glochiceras from the Middle Kimmeridgian (Beckeri Zone), and some of Waagen’s (1875) species of Haploceras (H. deplanatum and H. propinquum) as forms transient from Middle Kimmeridgian Glochiceras of the G. fialar group to the genus Hildoglochiceras, respectively. Spath (1928) described a single Haploceras sp. close to a juvenile H. elimatum (Oppel) from the Upper Tithonian (Transitorius Zone?) of the Umia Group (= Jhuran Formation). He envisaged recurrent homeomorphism in long-ranging haploceratins, which he interpreted as inhabitants of warm waters, and highlighted that the smooth inner whorls of the common Taramelliceras of the T. kachense group from the Middle Kimmeridgian (Eudoxus and Beckeri? zones) with ventral reliefs resemble Haploceras charactheis Zeuschner. Spath (1931) mentioned earlier revisions of the single specimen of Haploceras propinquum Waagen, regarded it as a form probably transient to Hildoglochiceras (Spath, 1928), and later reinterpreted it as Hildoglochiceras (Spath, 1933). Spath (1928) reinterpreted Haploceras propinquum Waagen and Haploceras dieneri Waagen as Hildoglochiceras, and Haploceras cf. tomephorum Zittel to be a juvenile aspidoceratin. This author identified the Haploceras beds of Gudjinsir as the base of his Portlandian, with several species assigned to Hildoglochiceras, recognized Haploceras elimatum (Oppel) as the most common component in the Gudjinsir fauna of Kachchh, and among Kachchh species of Alpine-Mediterranean affinity, and described Haploceras sp. ind. juv. from his Tithonian Umia beds. Pandey et al. (2016) cited Haploceras cf. tomephorum Zittel among Upper Tithonian ammonites reported from the Kachchh Basin by earlier workers. Krishna (2017) reported Haploceras cf. elimatum (Oppel) from his Natricoides Zone–Communis Zone, Communis Subzone, which he interpreted as corresponding to a 3^rd-order sequence with MFS in the Krafti Subzone, and correlated the Natricoides Zone with the Semiforme/Verruciferum Zone in Europe. Krishna identified the same stratigraphic interval and 3^rd-order sequence in Jaisalmer.

In Madagascar, Lemoine (1910) refused to use the taxon-name Haploceras and reported abundant specimens of Lissoceras deplanatum (Waagen), which he clearly distinguished from elimatum (Oppel) and staszycii (Zeuschner) and interpreted to be younger (Tithonian). This author did not illustrate his Madagascan deplanatum, thus the equivalence with the type of Waagen cannot be evaluated. Spath (1925a) reinterpreted Lissoceras deplanatum (Lemoine non Waagen s.) as Haploceras elimatum (Oppel), illustrated from his Kimmeridgian horizons of Antsalova, which according to Lemoine shows some affinity with Haploceras indicum Uhlig (1903: 21, pl. 3, fig. 2a, b), a form that could be better interpreted as closer to Haploceras staszycii (Zeuschner). Spath (1925b) interpreted Haploceras elimatum (Oppel) as the most abundant ammonite in the undescribed collection from Madagascar, but had reservations concerning the high degree of similarity envisaged between ammonite faunas of Madagascar and Kachchh. Spath (1928) reconsidered the suture of his Haploceras elimatum (Oppel) from Madagascar (Spath 1925a) as being closer to that shown by Sicilian specimens of Haploceras staszycii Zeuschner. Spath (1928) mentioned Haploceras elimatum (Oppel) from the Besaire Collection, and recognized its low value for precise age-interpretations given its long stratigraphic range, as well as its common occurrence with Hildoglochiceras kobelli and latistrigatum at Antsalova. He also mentioned Haploceras staszycii (Zeuschner) from the same collection, recorded west of Mampikony, and highlighted the similarity among Madagascan ammonite assemblages and those known from Tendaguru (Tanzania), Kachchh, and Spiti. Collignon (1960) stressed the affinity of Tithonian faunas from Madagascar with those from Kachchh, Spiti, Kurdistan, SW Europe, and NW Africa, and described and illustrated diverse haploceratins from Lower Tithonian Kobelli Zone (Madagascar), including Haploceras gr. elimatum (Oppel) – subelimatum Fontannes, and Haploceras staszycii (Zeuschner). This author also reported Glochiceras deplanatum Waagen, which he interpreted as inconclusively known and comparable to smooth inner whorls of the more evolute Hildoglochiceras, and difficult to distinguish from inner whorls of Haploceras elimatum, except for the suture line.

Southwards along the western margin of the Trans-Erythraean Trough, Howarth and Morris (1998) reported Haploceras stascyzii (Zeuschner) from a 5 m interval with Upper Kimmeridgian perisphinctins and taramelliceratins at Wadi Arus, southern Yemen, and interpreted their Kilya Member to represent the Upper Kimmeridgian Beckeri Zone to Lower Tithonian Hybonotum Zone, while their new species Haploceras umbilicatum was recorded together with probable uppermost Tithonian to Lower Berriasian ammonites. No Haploceras were reported by Zeiss (1971, 1984) from Ethiopia, and no reports are available from Somalia. In Kenya, Haploceras seems to be absent (Beyrich 1877), or it was rare, because Haploceras elimatum (Oppel) early on recorded further south from the Trigonia smeei Beds at Tendaguru, Tanzania (Zwierczyki 1914), was interpreted as Lissoceras (Dietrich 1925, 1933; Spath 1925a, 1933; Bussert et al. 2009). Kapilima (2003) too did not report Haploceras from Tanzania.

Based on the preceding revision, the record of Haploceras staszycii (Zeuschner) – elimatum (Oppel) from the Hildoglochiceras kobelli Zone of Madagascar (Early Tithonian of Collignon 1960) cannot be used for a conclusive, regional age-interpretation in the Trans-Erythraean Trough, where its precise stratigraphy is unknown. However, the described specimens are interpreted to represent Lower Tithonian (three-fold division) horizons in accordance with the biostratigraphic interpretation of the here described Hildoglochiceras, a single specimen of Aulacosphinctoides and an incomplete virgatosphinctin.

Two specimens, Hildoglochiceras Bed of Jara Dome (Lower Tithonian); KSKV2019Jara/65, 67 (both figured).

Shell small, incomplete, compressed, involute subquadrangular whorl section with almost flat to slightly arched lateral surface, slightly arched ventral region, indistinct umbilical shoulder and short, steeply sloping umbilical wall.

These are moderately preserved, small specimens that show abraded external surfaces. Specimen no. KSKV2019Jara/65 consists of the phragmocone and body chamber, whereas specimen no. KSKV2019Jara/67 is only a part of the body chamber. Except for the umbilical diameter, which is larger in the present specimen, other dimensional proportions are within the range of variation in Haploceras staszycii (Zeuschner) (Fig. 7), however, the subquadrangular whorl section and the umbilical diameter do not match any of the specimens of the present collection nor the species of Haploceras described by Waagen and Collignon, most probably due to their small size.

The genus Haploceras shows a long biostratigraphic range from the latest Kimmeridgian to Early Berriasian. The interpreted age of the described specimen is Early Tithonian (three-fold division), in accordance with the biostratigraphic interpretation of described Hildoglochiceras, Aulacosphinctoides and an incomplete virgatosphinctin.

Hecticoceras latistrigatum Uhlig, 1903.

23 specimens, Hildoglochiceras Bed of Jara Dome (Lower Tithonian); KSKV2019Jara/1–9, 21, 26, 32, 41, 45, 46, 48–51, 54, 55, 74, 75, KSKV2020Jara/15.

Shell small consting of both phragmocone and body chamber with maximum shell diameter of ca. 50 mm (KSKV2020Jara/15), nearly complete, discoidal, compressed and evolute. Whorl section narrow subtrigonal to oval with narrow venter. Lateral sulcus at lower one-third of lateral height to mid-lateral height, wide, and terminates just above the base of the ventral branch of the peristome. Lateral surface flat, ornamented with faint sickle-shaped (falciform) ribs on the body chamber (e.g., KSKV2019Jara/1). A shallow spiral groove situated at one-third to one-half of the flank height of both phragmocone and body chamber. Spiral groove gradually changing in width with growth. Lower boundary of spiral groove higher than upper boundary (Fig. 6R, S), coinciding with maximum shell thickness. Inner, dorsal one-third of body chamber, i.e. area below the spiral groove, sloping towards umbilical seam with broadly arched umbilical shoulder region and steep umbilical wall. Peristome with lappets preserved. Suture lines well preserved, with denticulated lobes and saddles. Lobes slightly narrower than saddles (Fig. 6Q). First lateral lobe deep, moderately broad, with three short branches at the end. Second lateral lobe much shorter. At least two auxiliary lobes above the umbilical suture. First (external) saddle broad and short, with small secondary lobes. The last two suture lines are very close, almost touching.

48 specimens, Hildoglochiceras Bed of Jara Dome (Lower Tithonian); KSKV2019Jara/10–16, 19, 20, 22–25, 27–31, 33–40, 42–44, 47, 52, 53, 56–60, 70–73, 76–78, 81, KSKV2020Jara/11, 12, 14.

Shell moderately large, consting of both phragmocone and body chamber with maximum shell diameter of ca. 95 mm (KSKV2020Jara/14), discoidal, compressed and evolute. Whorl section narrow subtrigonal to oval with narrow venter. Lateral sulcus at lower one-third of lateral height to mid-lateral height. Lateral surface flat, ornamented with sickle-shaped (falciform) or crescentic ribs, also seen on the juvenile specimens (Fig. 8A–E, H–L). The beginning of ribs variable, may start at a diameter less than 10 mm or even at diameter less than 4 mm. A shallow spiral groove situated at one-third to one-half of the flank height of both phragmocone and body chamber. Spiral groove gradually changing in width with growth. Spiral groove begins at a diameter less than 10 mm. Lower boundary of spiral groove higher than upper boundary, coinciding with maximum shell thickness. Inner, dorsal one-third of body chamber i.e., area below the spiral groove, flattened with obtusely rounded umbilical shoulder and steep to almost vertical umbilical wall (Fig. 10I). Suture lines moderately well preserved.

The specimens are moderately preserved and abraded. In some cases, they consist of phragmocone and almost a complete or a part of body chamber, in few cases (e.g., KSKV2019Jara/1, 5) half a whorl of body chamber (180°) with preserved aperture . Several specimens are very small with their body chambers preserved. They are juveniles (e.g., KSKV2019Jara/39–44). The specimens represent internal moulds, i.e., without shell material and ventral keel, even in the smaller specimens. The ornamentation is mostly no longer preserved, similarly, the wide and moderately deep lateral groove in some cases is partially preserved on the body chamber, but unidentifiable in the phragmocone.

The morphological features described above match Hildoglochiceras Spath, 1924. The general absence of population size analyses of species described in the literature impedes their precise interpretation in terms of intra-species variability. Hence, the maintenance of species names is obligatory in the present analysis.

The dimensional proportions of different species of Hildoglochiceras Spath, 1924 described from the Indo-Malagasy faunal province by the earlier workers suggest comparable H/D, T/D and H/T ratios (H/D: 33–45%; T/D: 21–28%; H/T: 1.32 to 1.8). However, U/D ratio is increasing from 29 to 42% (Table 3), except for few specimens that should be rechecked for their measurements and/or identification. Interestingly, in the present collection, shell diameter and the diameter of the umbilicus distinctly show two groups; type 1: small shell diameter with large umbilicus (U/D: 40 to 25%) and type 2: large shell diameter with small umbilicus (U/D: 26 to 18%). H/T is smaller (1.3–1.8) in type 1, whereas it is greater (1.35–2.0) in type 2 (Table 4). In general, WSG and HSG show a trend of values increasing with shell size. Based on similarity in morphological features type 1 is considered here as microconch (small shell diameter and larger umbilical diameter) with lappets (only their bases are preserved just below the adapertural end of the lateral groove (Figs 6P, 8F), and type 2 as macroconch (large shell diameter and smaller umbilical diameter) without preserved peristome. However, both types are also represented by juvenile specimens (e.g., KSKV2019Jara/39–44).

Hildoglochiceras latistrigatum (Uhlig, 1903) matches present specimens in having a similar shape including whorl section and a maximum width along the lower lip of the lateral groove, but has a wider umbilical diameter (Uhlig 1903: 27, pl. 2, fig. 4; pl. 3, fig. 5; Pandey et al. 2016: 146, pl. 1, fig. 2a, b). Lacking data at the population level, no conclusion about the meaning of this difference can be drawn. The species has been reported ornamented with distant sickle-shaped ribs and growth striations, however, the ornamentation is variable and inner whorls are smooth.

Uhlig (1903: 28), while describing his new species Hildoglochiceras latistrigatum, mentioned that the growth striations follow a similar pattern as in H. kobelli. Further he mentioned H. latistrigatum “approximates very closely to H. kobelli” Oppel but the differences between the two species make it impossible to merge them (Table 5). In fact, most of the characters mentioned are relative and thus are not tenable when several specimens are compared. Nevertheless, of several differences mentioned by Uhlig, the present specimens are closer to Hildoglochiceras latistrigatum in ornamentation. Unfortunately, Uhlig did not mention a larger diameter of the umbilicus in H. latistrigatum in comparison to H. kobelli, which is one of the distinctive characters.

The line of maximum inflation either along the upper or lower margin of the spiral furrow cannot be a distinguishing feature between H. kobelli and H. latistrigatum, because in one of the figures of H. kobelli from Madagascar (Lemoine 1910: 146, pl. 4, figs 1–4, and apertural view figured at https://science.mnhn.fr/institution/mnhn/collection/f/item/r02008) it is clearly along the lower margin of spiral furrow. In juvenile forms (KSKV2019Jara/30, 40, 42), the elevation of the lower boundary of the spiral groove, whether higher or lower than upper boundary, may not be ascertained.

The morphological characters in the present specimens match Harpoceras kobelli Oppel (Waagen 1875: 72, pl. 13, fig. 12 , non figs 11, 13), from the “Upper Katrol Group”, south-west of Nurrha, in having similar proportional dimensions, but differ in having the maximum thickness of the whorl along the upper boundary of spiral groove, instead of along its lower boundary. Spath (1928: 159, pl. 13, fig. 17) mentioned the observation of Waagen (1875: 73, pl. 13, figs 11–13) and Lemoine (1910: 10 pl. 4, fig. 1–4) that H. kobelli Oppel is a very variable species with respect to the start of crescentic ribs (at a diameter of 25 mm or 30 mm or even later), number and sharpness/thickness of ribs and width of lateral groove, which gradually widens with growth. The present specimens match well with such observation (Fig. 8C–E, H, I, K, L). According to Lemoine (1910: 10), H. kobelliforme (Bonarelli) and H. latistrigatum (Uhlig, 1903) are mere varieties of the same species. In fact, Lemoine (1910) was pioneer in highlighting the identification of the great variability within Hildoglochiceras. According to Lemoine, H. kobelliforme has an “abrupt margin of the shell”, perhaps he meant an abrupt umbilical edge, H. latistrigatum shows a very wide furrow and H. kobelli has a less abrupt edge of the shell and a narrower furrow.

According to Spath (1928), H. kobelli Oppel and H. kobelliforme (Bonarelli) are morphologically similar. Further, Spath synonymised one of the specimens of Waagen (year) assigned to Harpoceras kobelli Oppel (Waagen 1875: 72, pl. 13, fig. 12) with Hildoglochiceras kobelliforme (Bonarelli). The suture line of this specimen (Spath 1928: 159, pl. 13, fig. 17) matches the suture lines of the present specimens. The other two specimens figured by Waagen as Harpoceras kobelli (Oppel) (Waagen 1875: 72, pl. 13, figs 11, 13) show either a lateral groove closer to umblical shoulder or a more transversely ovate whorl section.

Oppelia plana Waagen (1875: 56, pl. 11, fig. 3) from the “Katrol Group” (Kimmeridgian), south-west of Nurrha, is another comparable species with respect to its discoidal shape, proportional dimensions including umbilical diameter, smooth flanks with wide lateral groove and suture lines [see Hildoglochiceras ? planum (Waagen) (Spath 1928: 160–161, pl. 19, fig. 5) at a diameter of 20 mm of Waagen’s holotype (1875: 56, pl. 11, fig. 3) to Hildoglochiceras kobelliforme (Bonarelli)], but it has an oval whorl section with a rounded ventral region. Moreover, the present specimens are sculptured. The possibility of obliteration of ribs of the body chamber prior to final burial or general due to poor preservation due to weathering cannot be ruled out, especially as the matrix is a calcareous coarse-grained sandstone. Moreover, some doubts arise about the type described by Waagen (1875) since this author indicated “specimen with body chamber” in his figure caption, while Spath (1928, p. 160) stated that the “…fragmentary example described by Waagen is entirely septate and represents the inner whorls of a larger form, probably of the kobelli group entirely septate there…”. The Madagascan specimens assigned to Hildoglochiceras planum (Waagen) (Collignon 1960: pl. 144, figs 558–560) are very close to Hildoglochiceras kobelliforme (Bonarelli), if the smooth shells are a result of abrasion or due to preservation like in most of the present specimens. Spath (1928: 160) raised doubts about species level separation of Haploceras (Hecticoceras) spira Zwierzycki from Tendaguru, Tanzania (1914: 49, pl. 5, figs l l –13) from H. kobelliforme Bonarelli. Based on morphological similarity and dimensional proportions (Table 3) including the umbilical diameter, the specimens assigned to Hildoglochiceras kobelli Oppel by Collignon (1960: pl. 143, figs 547–550) are identified as H. kobelliforme Bonarelli herein. Hildoglochiceras nudum Collignon (1960: pl. 145, fig. 567; D: 43, H: 19 (44), T: 12(28), U: 10 (23)) is similar in discoidal shape, presence of a feeble spiral groove and dimensional proportions including umbilical diameter to the present specimens assigned to H. kobelli Oppel, which is a macroconch. From the illustrations (Collignon 1960: pl. 143, fig. 567) ribs along the periphery can be clearly seen. In all probability Hildoglochiceras nudum Collignon is a junior synonym of H. kobelli Oppel. Similarly, Glochiceras deplanatum (Waagen) (Spath 1928: 155, pl. 16, fig. 3, pl. 17 figs 9a, b) shows a comparable discoidal shape, lateral spiral groove, peripheral ornamentation and proportional dimensions including a similar umbilical diameter (Spath 1928: pl. 17, fig. 9; D: 70, H/D: 45 T/D: 24, U/D:·24; pl. 16, fig. 3; D: 67, H/D: 44, T/D: 25, U/D: 24) to the present specimens assigned to H. kobelli Oppel (1863b).

Contextually, the Madagascan taxa H. planum (Waagen) (Collignon 1960) (m), Haploceras (Hecticoceras) spira Zwierzycki (1914) (m), H. nudum Collignon (1960) (M), and Glochiceras deplanatum (Waagen) (Spath1928) (M) may be individuals of the dimorphic pair of the species discussed here, based on the assumption of a wide intra-species variability affecting mainly, but not exclusively, the lateral and ventral sculpture. This is in accord with the interpretation made by Collignon (1960) of the species Hildoglochiceras kobelli Oppel, including his new var. madagascariensis, and contrasts with his generally typological approach resulting in species-rich ammonite assemblages.

Hildoglochiceras sp. aff. kobelliforme (Bonarelli) (Énay 2009: 84, pl. 1, fig. 6a, b) shows similar dimensional proportions, and occlusion of the lateral groove in the umbilicus, but the sculpture is well developed.

Data from Pakistan are difficult to evaluate due to their poor preservation (Hildoglochiceras sp. ind. group of propinquum Waagen sp.; Spath 1939, pl. 18, fig. 8a, b) and the lack of body chamber (Hildoglochiceras cheemaensis Fatmi, 1973, pl. 3, figs 10–12). The latter is a large, septate form that, at equivalent shell size, shows a similar whorl height, but a lower degree of coiling in comparatively flattish, narrower shells with smooth phragmocone, a wide lateral groove below the line of whorl overlapping showing an inner, crescentic edge, and decreasing depth adaperturally, and a low arched, wide venter without keel.

Concerning the species under study, scanning through descriptions and figures of the species mentioned above given by earlier workers (Oppel 1863b; Waagen 1875; Bonarelli 1894; Uhlig 1903; Lemoine 1910; Spath 1928; Collignon 1960; Énay 2009: pl. 1, fig. 6a, b), it is evident that H. kobelli (Oppel), H. kobelliforme (Bonarelli), and H. latistrigatum (Uhlig) are morphologically very close. In view of the larger umbilical diameter of H. latistrigatum (Uhlig), the present specimens have been assigned to the H. kobelli (Oppel) (M) and H. kobelliforme (Bonarelli) (m) group. It may be mentioned here that Énay (2009: 84, pl. 1, fig. 6a, b), in the description of Hildoglochiceras sp. aff. kobelliforme (Bonarelli), mentioned it as Hildoglochiceras cf. kobelliforme (Bonarelli) in the caption on page 248. The statistical analysis of Hildoglochiceras is given in chapter 5 (see below).

Uhlig (1903, 1910) described the species of Hildoglochiceras from the Spiti Shales at Chidamu in the Himalayas of northern India. According to Spath (1933: p. 673), Hildoglochiceras latistrigatum (Uhlig 1903) from Spiti may be associated with the Aulacosphinctoides fauna (for the Natricoides Subzone see Pandey and Krishna 2002; Pandey et al. 2010), which had almost disappeared when Virgatosphinctes became dominant in the Early Tithonian.

Data from Spath (1939) and Fatmi (1972, 1973) indicate a generalized context of unconclusively known reworking in Pakistan. Limitations of the precise biostratigraphic interpretation of the Hildoglochiceras-rich horizon relates to the near-absence of precise information on Hildoglochiceras in particular sections and stratigraphic horizons elsewhere. In fact, despite usual correlations (since Uhlig 1903), the stratigraphic range of Hildoglochiceras (H. kobelli Oppel and related species) is inconclusively known, as rightly pointed out repeatedly by previous authors (e.g., Arkell 1956; Zeiss 1968; Énay 2009), or it is given as tentative in the most recent interpretation (Krishna 2017).

The biostratigraphic interpretation of the described Hildoglochiceras horizon is supported by the combination of local and region-wide observations (see above): (1) the absence of physical, stratigraphic features compatible with a wide stratigraphic gap in the section studied, but it could be inconclusive; (2) the local occurrence of transient forms between Neochetoceras and the Semiformiceras darwini Neumayr group in Nepal, the combined record of Hildoglochiceras and Paraboliceras in Himachal Pradesh (Spiti region, Himalaya), as well as by its rare record and tentative assignment to the lower part of the Virgatosphinctoides Zone at the Lakhapar section, Kachchh (Krishna et al. 1996); and (3) the common relationship between Hildoglochiceras horizons and transgressive pulses on epicontinental shelves across opposite palaeomargins of the Trans-Erythraean Through (India and Madagascar versus Tanzania). In this context, the present interpretation is compatible with the possibility of imprecisely known biostratigraphic differences between horizons of Hildoglochiceras from separate areas of the Tethyan embayment corresponding to the proto-Indian Ocean. An example of this can be the early report made by Waagen (1875) on his Haploceras propinquum Waagen – later interpreted as Hildoglochiceras (from Spath 1933 to Énay 2009) – as coming from the lowest beds of the Katrol Group, just above “oolitic deposits with Asp. perarmatum at the Keera Hill near Charee”. At first, this record would refer to the Kimmeridgian Group he correlated with Europe. This report would point to the Middle Kimmeridgian i.e., to the Eudoxus-Steraspis stratigraphic interval, according to Spath (1928), hence indicating records of the genus Hildoglochiceras older than usually interpreted, just above the stratigraphic gap envisaged by Spath (1933: table 1) for Kachchh. In addition, it may be noted that Paralingulaticeras-like forms resembling the groups of P. nodosum Berckhemer– P. parcevali Fontannes (subtly sculptured forms without and with lateral groove, respectively) and P. lithographicum Oppel (coarsely sculptured forms) are west Tethyan equivalents of comparatively stout shells of Paraglochiceras described and illustrated by Collignon (1960) from Kobelli Zone in Madagascar. These stouter forms are typical Madagascan “species”, when compared to west Tethyan equivalents.

In accordance with the biostratigraphic interpretation of the taramelliceratin phragmocone described herein and the review of interpretations of Hildoglochiceras records by paying attention to palaeoenvironmental and stratigraphic contexts, two Lower Tithonian intervals related to transgressive pulses are considered. These correlate with the upper to uppermost Hybonotum–lowermost Albertinum/Darwini Zone, and with the lower Semiforme/Verruciferum Zone in the European Standard Scale, respectively. The former would agree with the record of forms intermediate between Neochetoceras and early Semiformiceras, and it would be compatible with the occurrence of Parastreblites during a regression before the subsequent lowstand characterizing deposits corresponding to the Albertinum/Darwini Zone interval. The second would point to an increasing sea level after Albertinum/Darwini times during the younger range of Parastreblites. Older (latest Kimmeridgian) and younger (post-Semiforme/Verruciferum Zone) time intervals are discounted due to the lack of evidence of a wide stratigraphical gap below the Hildoglochiceras horizon in the section studied.

Two specimens, Hildoglochiceras Bed of Jara Dome (Lower Tithonian); KSKV2019Jara/17 (figured), 79.

Fragments of phragmocone of small size, moderately involute, compressed, with oval whorl section, indistinct ventro-lateral shoulders, and obtusely rounded ventral region. Ornamentation consisting of blunt, falcate, primary ribs with marked inflection slightly below the mid-flank. Swell at branching points at mid whorl height, along thin, faintly developed spiral groove. Secondary ribs crescentic, occasionally showing very subtle swellings that barely define the indistinct flank periphery and shoulders. Ventral region without identifiable ribs or tubercles. Suture lines relatively well preserved with smoothed peripheral frilling.

The first specimen (KSKV2019Jara/17), a small fragment of a phragmocone, ca. 50 mm in size is an internal cast with accentuated variably preserved flanks. The left side has been abraded, except for the extreme outer flank that shows remnants of blunt secondaries, while the right side shows remains of a moderately coarse ornamentation across the flank, with a shallow and discontinuous lateral groove-like depression and selective collapse areas. The ventral region is unornamented, subtly raised on the mid-line, and flanked by the external ends of ribs, some of which show incipient oblique-radial swellings barely differentiated from the ribs, which do not contribute to the distinctness of shoulders. The state of preservation precludes any clear remains of tuberculation.

It seems that the right flank exhibits glochiceratin-taramelliceratin traits: (1) peripheral and widely spaced incipient swellings (“remains of tuberculation”?), occasionally located at points where two secondary ribs connect; and (2) a lateral groove-like depression slightly above the mid-flank. In contrast, the smoothed left flank preserves suture lines in such a way that attrition has been pervasive enough to distort ribbing severely and produced the peripheral frilling of septa; hence the suture-line smoothing corresponds to an erosion level being at least equivalent to rib thickness (compared with the sharper suture-line frilling preserved on the rightside). It is unclear whether differential preservation operated on a pathologic specimen (note symmetrical thickness of the internal cast with respect to the siphuncle) showing different lateral sculpture (Fig. 11A, B), or whether the present appearance merely is a taphonomic feature (comparatively smoothed left flank). The latter option would suggest weathering or reworking and abrasion. The latter would point to a distinct break in sedimentation and later bioturbation during renewed continuous deposition. Reworking is of special interest in the context of the biostratigraphic interpretation as commented in previous sections.

The taxonomic interpretation of incomplete oppeliids, as in the case of other Late Jurassic ammonites, is a very difficult task since diagnostic morphological features for identification at the genus and species levels only developed on middle and outer whorls, inner whorls being largely indistinct. This general pattern is taxon-dependent. This situation is accentuated when natural conditions (outcrop, deposition, preservation) and/or collecting limitations (sample size, sampling process) impede access to large samples from a given stratigraphic horizon, i.e., a particular bed representing continuous deposition during a relatively “short” time with no or only a low degree of within-habitat time-averaging. Overall, dominant depositional conditions in Kachchh during the Late Jurassic determined the rarity of records of large, “isochronous” ammonite samples enabling an analysis at the population level.

Based on the assumption that the lateral groove is real though defectively preserved, Paralingulaticeras may show a similar sculpture but it shows well-developed ventro-lateral tubercles, a much more slender, flatter shell with a lower degree of coiling, and the lateral groove is mainly developed on the body chamber. Among well-known European Paralingulaticeras species (cf. Ziegler 1958), P. nodosum Berckhemer with scarcely marked lateral groove and tuberculation, and the sparsely tuberculated P. parcevali Fontannes, are differently ribbed on the flanks, while the densely tuberculate and coarsely ribbed P. lithographicum Oppel clearly differs in shape and sculpture. These species of Paralingulaticeras occur in the latest Kimmeridgian Beckeri Zone and in the lowermost Tithonian, lower part of the Hybonotum Zone of Submediterranean (Ziegler 1958; Berckhemer and Hölder 1959) and Mediaterranean areas of the Western Tethys (Olóriz 1978; Caracuel and Olóriz 1999).

Among ornamented glochiceratins from eastern Gondwana, the Madagascan Paraglochiceras from the Hildoglochiceras kobelli Zone (interpreted as Early Tithonian in Madagascar) commonly have more globose shells with unsculptured inner flanks. P. hirtzi Collignon (1960: pl. 146, fig. 576) and P. aff. propinquum (Waagen) are relatively close in shape but clearly differ in sculpture. Hildoglochiceras shows ventrolateral ribs that rarely bifurcate in the more finely ribbed species and does not have any dorsolateral ribs. Hildoglochiceras colei Spath (Collignon 1960: pl. 144, fig. 561) shows slightly more flattened and convergent flanks, and different external ribs. H. parceumbilicatum parceumbilicatum Collignon (1960: pl. 144, fig. 563) curiously resembles the smoothed left flank of specimen described herein. Hildoglochiceras tenuicostulatum Collignon (1960: pl. 145, fig. 568) shows a more crowded and delicate ribbing. Aside from the usual schemes of correlation, the precise biostratigraphic range of the genus Hildoglochiceras is not conclusively known, as has been discussed above.

If alternatively, the lateral groove is a secondary, preservational feature, there are two interpretations of the inner cast described:

(1) Parastreblites Donze and Énay 1961, which does not possess a lateral groove, shows a streblitoid whorl section in the outer whorls, but its inner whorls could be similar in sculpture to the Taramelliceras compsum group, since the mid-flank tuberculation of Streblites does not occur (Olóriz 1978). In fact, this tuberculation reveals Taramelliceras inheritance s. str., excluding the group of Taramelliceras trachinotum Oppel (Donze and Énay 1961) due to its clearly older age. Parastreblites has been recorded in the Lower Tithonian (three-fold division) Darwini Zone and in the upper Hybonotum-Albertinum (=Darwini) Zone in the western Tethys (southern Spain; Énay and Geyssant 1975 and Olóriz 1978, respectively), but potential records from latest Kimmeridgian to earliest Tithonian horizons cannot be excluded, if Oppelia gaetanoi Fontannes is considered. Inner whorls of some species of Parastreblites show morphologic affinity to the group of Taramelliceras compsum (Oppel) (e.g., Parastreblites hoelderi in Donze and Énay 1961). In fact, Parastreblites has been reported from distant areas outside Europe (Imlay 1942; Donze and Énay 1961; Leanza 1980; Parent et al. 2015), but there it is a rare, inconclusively known taxon showing a distinct morphology and wider biostratigraphic range with respect to European specimens. Even allusions to the Kimmeridgian genus Metahaploceras have been made for those Lower Tithonian ammonites.

(2) Taramelliceras is the alternative option for interpreting the incomplete inner cast described. First revised by Hölder (1955), Taramelliceras exhibits a notable intra-species variability and is represented by three main species groups in the Upper Jurassic, with the T. compsum group as the source for Mid-to-Late Kimmeridgian forms and their youngest offsprings. According to Hölder (1955), the T. compsum group was widely distributed, from Mexico to India, and Taramelliceras (Metahaploceras) occurred throughout East Africa. All these data reveal a Tethyan influence in the surrounding epicontinental areas on both sides of the Trans-Erythraean Gulf or incipient seaway, during rising sea-levels throughout late Middle to Late Kimmeridgian and Early Tithonian times (three-fold divisions). Berckhemer and Hölder (1959) revised Malm ε to ζ₃ taramelliceratins from southern Germany and split the compsum group in subspecies, with diversified descendants during latest Kimmeridgian and earliest Tithonian times up to probably ζ₃ e.g., Taramelliceras franciscanum Fontannes, which was preliminarily included by Hölder (1955) in Taramelliceras compsum. Olóriz (1978) confirmed the pronounced morphological variability in Tethyan specimens of Taramelliceras compsum (Oppel) from the Betic Cordillera in southern Spain and highlighted the relevance of this species and related forms during the Late Kimmeridgian (two-fold division) and the earliest Tithonian. Working on better preserved material from epicontinental deposits with a continuous sedimentary record, Baudouin et al. (2011) were able to demonstrate a high within-species variability in a large sample of Taramelliceras compsum, collected from two successive beds in fine-grained siliciclastic-carbonate rhythmites of the Mount Crussol type-section, southern France. From Hölder (1955) to Baudouin et al. (2011), Taramelliceras compsum has been interpreted to be very variable with respect to ribbing and tuberculation, including its inner whorls. Commonly, two lateral ribs connect to a single ventro-lateral tubercle at a relatively small shell size; other specimens with broader and slightly domed vs. raised ventral regions have a virtually smooth to clearly tuberculate midventer, respectively. Taramelliceras kachchense Spath has been interpreted to be a derived form from across Trans-Erythraean Through areas, where references to the group of Taramelliceras compsum (Oppel) have been common from Uhlig (1903) onwards.

The strongly ribbed left side of the analysed phragmocone excludes comparison with smooth forms such as Taramelliceras nivale (Stolizcka), an insufficiently known species reported from Himalayan and Madagascan areas.

All this information supports the tentative interpretation of the incomplete phragmocone described as belonging to Taramelliceras sp. of the T. compsum (Oppel) – T. kachhense Spath groups. These two nominal species are most probably evidence of a Tethyan source and a local, derived taxon, respectively, the latter being a local phenotype expression related to colonization of shelves bordering the Trans-Erythraean Through. Thus, the biostratigraphic range of Taramelliceras could extend from Middle Kimmeridgian horizons to the lower part of the Lower Tithonian (three-fold-division), if the total range of the former species in west-Tethyan areas applies. Southwards, at the Indian-Malagasy palaeomargin, Collignon (1960) documented what he interpreted as Lower Tithonian Taramelliceras in Madagascar, but a more accurate biostratigraphy is needed before a definite conclusion can be reached, also with respect to its actual co-occurrence with Hildoglochiceras there, i.e., without reworking.

The stratigraphic range assumed for the Oppel species in west-Tethyan areas, with the youngest Taramelliceratinae occurring in the Albertinum/Darwini Zone, and the limited evidence of reworking in the stratigraphic interval sampled (a single specimen; see description above) points to the possibility that Taramelliceras occurs from levels with a minimum age of Early (earliest?) Tithonian (three-fold division). The assumed co-occurrence with Hildoglochiceras in Kachchh and Madagascar should be consistent with an age of the oldest Hildoglochiceras older than usually interpreted. The inconclusive evidence of lowermost Tithonian horizons in these areas could be the result of unfavourable conditions for ammonites and/or of stratigraphic gaps in connection with the change from coarse-grained siliciclastics to calcareous sediments. Apparently, regional tectonic forcing during earliest Tithonian times occurred close to the Jurassic eustatic maximum. Local variation in the time span involved in the stratigraphic gap cannot be dismissed in accordance with lateral facies changes of deposits containing Hildoglochiceras in the area (e.g., Pandey et al. 2016).

The alternative interpretation of the described phragmocone as Parastreblites sp. gr. hoelderi Donze and Énay (1961) is compatible with the biostratigraphic interpretation just proposed, based on the assumption that the biostratigraphic range of European Parastreblites (Parastreblites) s. str. is the reference for correlation, which might include the Ulmensis horizon (=uppermost Kimmeridgian or lowermost Tithonian according Donze and Énay (1961). However, even though being difficult to evaluate (e.g., Parent et al. 2011), the rare records of Parastreblites from the Zitteli Zone in Argentina (Leanza 1980; Parent et al. 2011, 2015; Vennari 2013) could be taken into account, but the illustration by Parent et al. (2015) of material collected from horizons above their Zitteli and Proximus zones rather excludes the assignment to Parastreblites s. str.

In the absence of age-diagnostic Tethyan and Indian ammonites in the reported ammonite assemblage, the Hildoglochiceras described here represent a local record but, being a sample of population size, it is the most relevant record of this genus that is available. The favoured biostratigraphic interpretation points to indeterminate upper Lower Tithonian horizons (three-fold division), correlated with a lower part of the Tethyan Albertinum/Darwini Zone, but slightly older horizons also might apply. This interpretation is based on: (1) underlying ammonite-poor, sandy deposits without evidence of relevant erosion at the top; (2) lacking records of Hybonoticeras, which are mainly interpreted to represent the uppermost Kimmeridgian across epicontinental deposits in the Trans-Erythraean Trough, and rarely lowermost Tithonian horizons; (3) the occurrence of transient forms between Neochetoceras and early Semiformiceras in neighbouring areas (Nepal), interpreted as probable evidence of morphological evolution towards early forms of Semiformiceras rather than a case of local, diachronous homeomorphism; (4) occurrence elsewhere in the Trans-Erythraean Trough of ammonites morphologically close to those belonging to Lower-to-lowermost Tithonian in West-Tethyan areas, and (5) the interpretation of the Hildoglochiceras horizon as recording a local maximum flooding zone. This interpretation agrees with the occurrence of ammonite remains morphologically close to virgatosphinctins, reported and illustrated with precise stratigraphic control (“Couches à Virgatosphinctes et Aulacosphinctoides” at Nupra, Thakkhola, central Nepal, by Énay (2009); and comments with precise citations in previous sections). The second alternative pointing to some horizons within the upper Albertinum/Darwini to lower Semiforme-Verruciferum zones is potentially correlatable with the early Middle Tithonian transgressive pulse in different areas worldwide but could involve a wider stratigraphic gap (Fig. 2).

Aulacosphinctes infundibulus Uhlig, 1910.

One specimen, Hildoglochiceras Bed of Jara Dome (Lower Tithonian); KSKV2020Jara/13.

Shell moderately large (ca. 55 mm in diameter), evolute and depressed. Whorl section subcircular with uniformly arched flanks, umbilical shoulder regions and broad venter. Ornamentation consists of prorsiradiate, biplicate ribs, branching above mid-lateral height into finer secondary ribs, crossing ventral region almost straight. Primary ribs thick, moderately spaced, originating from umbilical suture slightly rursiradially. Occasionally, single primary rib. Constrictions seen on inner whorls. Umbilical wall steeply inclined.

The outer whorl represents the body chamber, filled with micrite with dispersed coarse quartz grains. There is no sign of any suture lines. The specimen is slightly deformed showing an almost flat right lateral surface with maximum inflation at the ventro-lateral shoulder, whereas the left lateral surface is uniformly arched with the region of maximum inflation at mid-lateral height. The depressed whorl section, biplicate thick ornamentation and presence of constrictions in the inner whorls suggest the genus Aulacosphinctoides Spath. Due to the fragmented and deformed nature of the specimen a species identification is not possible. Nevertheless, the morphological characters are comparable with Aulacostephanoides infundibulus (Uhlig 1910: 371, pl. 66, fig. 3a–c, pl. 72, figs la–c (= lectotype), 2a–c, 3a, b, 4a–c; Yin and Énay 2004: pl. 3, fig. 7a, b; Énay 2009: 181, pl. 42, fig. la–c).

The Aulacosphinctoides or Virgatosphinctes and Aulacosphinctoides assemblage suggests an earliest Tithonian age (see above) (Uhlig 1903, 1910; Spath 1933: 673; Pathak 1997, 2007; Pandey and Krishna 2002; Yin and Énay 2004; Énay 2009; Pandey et al. 2010, 2013).

One specimen, Hildoglochiceras Bed of Jara Dome (Lower Tithonian); KSKV2019Jara/80.

Shell large (the fragment is approximately 9 cm in diameter and judging by its curvature represents around one-fourth of the phragmocone with a possible final diameter of 13 cm), evolute, slightly depressed (H: 35, T: 40.7, H/T: 0.85) or (H: 40, T: 41.6, H/T: 0.96) suboval whorl section with distinct but obtusely rounded umbilical shoulder, steep umbilical wall, lateral surface that converges smoothly in the obtusely rounded ventral region. Maximum whorl thickness slightly above umbilical shoulder. Ornamentation consisting of distant, thick, prorsiradiate, fascipartite/fasciculate ribs. Primary ribs originating from umbilical wall rursiradially, bending prorsiradially at umbilical shoulder, displaying a slight forward concavity on lateral surface, branching into thin, densely crowded five to six secondary ribs at mid-lateral height. Secondary ribs following the same course as primary ribs, one or two free secondary ribs inserted between adjacent primary ribs, maximum number of secondaries produced by a single primary rib may not exceed seven. Secondary ribs crossing ventral region with slight forward-directed sinuosity.

The specimen represents a small fragment of the phragmocone with moderately preserved suture lines. Due to the fragmentary nature, ornamentation of inner whorls and of the body chamber is not known. The distant, thick, prorsiradiate, fascipartite/fasciculate ribs with forward-directed concavity on the lateral surface, branching into several fine secondary ribs, the suboval whorl section and H/T ratio are similar to Perisphinctes (Virgatosphinctes) minusculus Uhlig (1910: 317, pl. 56, fig. 2a–c; D: 108, H: 32, T: 36, H/T: 0.88, U: 47). However, the number of secondary ribs produced by one primary rib ranges from 9–10 instead of up to seven in the present specimen.

The ornamentation and whorl section of the outer whorl also match Perisphinctes (Virgatosphinctes) raja Uhlig (1910: 316, pl. 50, fig. 1a–d), but P. (V.) raja has a thicker shell (D: 143, H: 49, T: 57, H/T: 0.85, U: 58.3) and distant ribs in the inner whorls. The H/T ratio in the present specimen is intermediate between the two species discussed above (see also Uhlig 1910: 318).

No true virgatotomy s. str. is recognizable in the present specimen, and divisions seem to be rather fascipartite/fasciculate. Since 5–7 secondaries occur in particular divisions on the phragmocone, a greater number could be expected on the body chamber.

This fragment of phragmocone is too incomplete for a conclusive interpretation. The significant feature is the wide-oval whorl section, which rarely occurs in typical Virgatosphinctes, if Énay’s (2009) classification is assumed (even with caution). Virgatosphinctes sp. C (Énay 2009: 168, pl. 32, fig. 4) is the only species showing a wide-oval whorl section, but its ribbing seems to be more crowded and with shorter primary ribs (Énay 2009: pl. 33, fig. 3). Also of interest is its early proliferation of secondary ribs, and the provenance from the “Couches à Virgatosphinctes et Aulacosphinctoides” at Nupra, in assumed Lower Tithonian below Nepalese Hildoglochiceras beds.

Uhlig (1910) described the two species mentioned above without precise stratigraphy from Spiti and Chidamu areas, respectively. Based on the assemblage recorded here, the comparative analysis with species of known stratigraphy, and the proposed biostratigraphic interpretation for the Hildoglochiceras described, the specimen is assigned to indeterminate horizons within the Lower but not lowermost Tithonian (three-fold division), correlated with indeterminate horizons within the lower part of the Tethyan Albertinum/Darwini Zone, less probably with the upper Darwini to lower Semiforme-Verruciferum zones (Fig. 2).