Aulacosphinctoides sp. ind.

Pandey, Dhirendra Kumar, Fuersich, Franz T., Alberti, Matthias, Das, Ranajit & Saez, Federico Oloriz, 2022, First population-level study of the ammonite genus Hildoglochiceras Spath, and the Lower Tithonian record of the Hildoglochiceras Horizon in the Kachchh Basin, India, Zitteliana 96, pp. 1-49 : 1

Aulacosphinctoides sp. ind.

Fig. 11G-I

Material.

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

Description.

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.

Remarks.

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).

Biostratigraphy.

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).

Figures

Figure 11. A-F. Taramelliceratinae gen. and sp. ind. KSKV 2019 Jara / 17. A. Internal cast, left side view of a fragment of phragmocone showing remnants of blunt secondaries along the periphery; B. Right side view showing moderately coarse ornamentation across the flank, with a shallow and discontinuous lateral groove-like depression and selective collapse areas; C. Suture line drawn from right lateral side, showing smoothed peripheral frilling; D. Line diagram showing oval whorl-section; E. Apertural view; F. Ventral view showing unornamented, subtly raised on the mid-line, and flanked by the external ends of ribs, some of which show incipient oblique-radial swellings; G-I. Aulacosphinctoides sp. ind. KSKV 2020 Jara / 13; G. Ventral view showing broad ventral region, sedondary ribs crossing ventral region almost straight; H. Enlarged right side view of inner whorls (nucleus) showing moderately thick prosiradiate ribs and constrictions; I. Right side view of body chamber showing regularly bifurcating and occasionally, single primary rib, the nucleus part is represented by mould of the cast shown in fig. H; J-L. Virgatosphinctes s. l. sp. KSKV 2019 Jara / 80; J. Line diagram showing suboval whorl section with obtusely rounded ventral region, distinct but obtusely rounded umbilical shoulder and steep umbilical wall; K. Right side view showing distant, thick, prorsiradiate, primary ribs branching into thin, densely crowded five to six secondary ribs at mid-lateral height and displaying a slight forward concavity; L. Ventral view showing broadly rounded ventral region and secondary ribs crossing ventral region with slight forward-directed sinuosity.