Foordiceras eicosacanthum Korn & Hairapetian, 2025, sp. nov.

Foordiceras eicosacanthum sp. nov. urn:lsid:zoobank.org:act: 439D1047-04C8-45E8-A26D-7B8F74784441 Fig. 16; Table 10 Endolobus sp. – Korn et al. 2021: text-fig. 17a. Diagnosis Species of Foordiceras with thickly discoidal, evolute conch (ww/dm ~0.47; uw/dm ~0.47), moderately depressed whorl profile (ww/wh ~ 1.75) and moderately high coiling rate (WER ~ 1.80) at a conch diameter of 60 mm. Whorl profile rounded trapezoidal with strongly divergent, flattened flanks; venter flattened. Sculpture with about 20 weak, blunt ventrolateral ribs per volution. Suture line with a very wide and shallow external lobe and a very shallow, broadly rounded lateral lobe. Etymology From the Greek ‘εἴκοσι’=‘twenty’ and ‘ἄκανθα’=‘thorn, spine’; because of the 20 ventrolateral nodes. Type material Holotype IRAN – Esfahan Province • Baghuk Mountain; Hambast Formation, Vedioceras beds (late Wuchiapingian); 2013; Korn et al. leg.; illustrated in Fig. 16A–C; MB.C.30223. Paratype IRAN – Esfahan Province • 1 specimen; same data as for holotype; 2011; Korn et al. leg.; illustrated in Fig. 16D–F; MB.C.32123. Description Holotype MB.C.30223 is an incomplete internal mould with a conch diameter of 57 mm; it is fully chambered (Fig. 16B). The conch width had to be reconstructed; it appears that the conch is thickly discoidal and subevolute (ww/dm ~0.48; uw/dm= 0.47) with a moderately high coiling rate (WER= 1.81). The whorl profile is moderately depressed (ww/wh ~ 1.80) and rounded trapezoidal with a flatly rounded venter and a broadly rounded ventrolateral shoulder. The divergent flanks are slightly flattened; an umbilical margin is not present (Fig. 16A). The sculpture consists of low conical ventrolateral nodes, of which there are 10 on half a volution. They are entirely confined to the ventrolateral shoulder and the outer flank and are as wide as their interspaces. The suture line shows a very wide, very shallow external lobe and a very shallow lateral lobe (Fig. 16C). The septa are rather short in the last quarter volution of the phragmocone has about eight chambers (CLI =11); in the penultimate volution, there are only six chambers on a quarter whorl (CLI=15). Paratype MB.C.32123 is a partially corroded specimen with a conch diameter of 68 mm (Fig. 16E). One whorl between a conch diameter of 20 and 37 mm is rather well-preserved and allows the study of the conch geometry and sculpture. In both features as well as in the suture line (Fig. 16F) the paratype agrees well with the holotype. The number of chambers remains the same in the last volution; in both last half volutions the phragmocone has 15 chambers each (CLI=12). The third last half volution has 12 chambers (CLI =15). Remarks Foordiceras eicosacanthum sp. nov. differs from F. decacanthum sp. nov. and F. ascetum sp. nov. in the rather small and more numerous ventrolateral nodes, of which there are ten on half a volution, while there are only five very coarse nodes on half a volution in the other two species. Furthermore, F. eicosacanthum has a more strongly depressed whorl profile (ww/wh ~ 1.75) than F. decacanthum (ww/ wh ~ 1.25) and F. ascetum (ww/wh ~1.00).