Serometacoceras inflatum, Korn & Ghaderi, 2025

Serometacoceras inflatum gen. et sp. nov.

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Fig. 22 View Fig ; Table 12 View Table 12

Metacoceras dorashamense – Teichert & Kummel 1973: 416, pl. 4 figs 5–6.

Diagnosis

Species of Serometacoceras gen. nov. with thickly discoidal, subinvolute conch (ww/dm ~ 0.55; uw/dm ~ 0.28), weakly depressed whorl profile (ww/wh ~ 1.30) and very high coiling rate (WER ~ 2.55) at a conch diameter of 40 mm. Whorl profile rounded-pentagonal with broadly rounded venter and flattened, gently divergent flanks and subangular umbilical margin. Sculpture with about 15 short lateral ribs per volution. Suture line with broadly rounded external saddle and shallow, broadly rounded lateral lobe.

Etymology

From the Latin ‘ inflatum ’ (adjective, n.) =‘inflated’; because of the ventrally inflated whorl profile.

Type material

Holotype

IRAN – West Azerbaijan • Aras Valley ; Araxoceras Beds of the Julfa Formation ( early Wuchiapingian); 2018; Ghaderi leg.; illustrated in Fig. 22 View Fig ; MB.C.32051 .

Description

Specimen MB.C.32051 is a fully chambered fragment almost 180 degrees long; the diameter of the conch is 40 mm ( Fig. 22A View Fig ). It is an internal mould partially covered by a tabulate reptant coral. The specimen has been ground to obtain a cross section of the conch and shows two volutions. The conch is thickly discoidal and subinvolute (ww/dm ~ 0.55; uw/dm ~ 0.28) with a weakly depressed whorl profile (ww/wh ~1.30) that shows a rather deep concave zone ( IZR ~ 0.15). The calculated coiling rate is extremely high (WER ~ 2.55). At a conch diameter of 40 mm, the whorl profile is characterised by a broadly rounded venter that merges continuously into the flanks, a pronounced umbilical margin and a flat umbilical wall, which is arranged perpendicular to the plane of symmetry. One volution earlier, the whorl profile is depressed rectangular (ww/wh ~ 1.60) with a rather well-defined ventrolateral shoulder.

The sculpture consists of short and rather coarse, blunt ribs on the flank; these ribs are weakly strengthened on the outer flank and form radially elongated conical nodes. The suture line shows a broadly rounded saddle on the venter and a broadly rounded lobe on the flank. The last half volution shows eleven chambers of the phragmocone. The septa are rather widely arranged; they are spaced at intervals averaging about 16 degrees.

Remarks

Although only one newly collected specimen is available, a new species is described for the very distinctive conch shape. Serometacoceras inflatum gen. et sp. nov. differs from the other species of the genus mainly by the short ribs in the middle of the flank. In contrast to the other species of the genus, these ribs are only very slightly thickened in the ventrolateral area. Another distinguishing feature is the broadly rounded venter. Only S. verae gen. et comb. nov. is similar in this respect, but this species is distinguished by a sculpture with rows of conical tubercles. Furthermore, S. inflatum is narrower umbilicate (uw/dm ~0.28) than S. verae (uw/dm ~0.33) at a conch diameter of 40 mm.