Domatoceras myloide, Korn & Hairapetian, 2025

Domatoceras myloide sp. nov.

urn:lsid:zoobank.org:act:

Fig. 4 View Fig ; Table 1 View Table 1

Diagnosis

Species of Domatoceras with thinly discoidal, subevolute conch (ww/dm ~0.35; uw/dm ~0.35), weakly compressed whorl profile (ww/wh ~ 0.90) and very high coiling rate (WER ~2.45) at a conch diameter of 70 mm. Whorl profile with weakly flattened venter, rounded ventrolateral shoulder, flattened and nearly parallel flanks, subangular umbilical margin and steep and flat umbilical wall. Whorl overlap very small. Without sculpture. Suture line with a small and very shallow external lobe and a much larger and deeper, broadly rounded lateral lobe.

Etymology

From the Greek ‘μυλοειδής’=‘millstone-shaped’; because of the conch shape.

Type material

Holotype

IRAN – Esfahan Province • Baghuk Mountain ; Hambast Formation, Araxoceras beds ( early Wuchiapingian); 2011; Korn et al. leg.; illustrated in Fig. 4 View Fig ; MB.C.32101 .

Paratypes

IRAN – Esfahan Province • 3 specimens; same data as for holotype; 2010; Korn et al. leg.; MB.C.32102 to MB.C.32104.

Description

Holotype MB.C.32101 is a fully chambered internal mould specimen with a conch diameter of 72 mm, which allows the study of one whorl ( Fig. 4B View Fig ). The conch is thinly discoidal and subevolute (ww/ dm =0.35; uw/dm=0.34) with an extremely high coiling rate (WER =2.47); the whorl profile is weakly compressed (ww/wh =0.90) with a weakly flattened venter, a rounded ventrolateral shoulder, flattened and almost parallel flanks, a subangular umbilical margin and a flattened and steep umbilical wall. The whorl overlap is very small ( IZR =0.06) ( Fig. 4A View Fig ). The internal mould appears to be completely lacking sculpture. The suture line is typical for the genus with a shallow external lobe and a much larger and deeper lateral lobe ( Fig. 4C View Fig ). The last half volution of the phragmocone has about 16 chambers (CLI=11).

Remarks

Domatoceras myloide sp. nov. differs from D. canonium sp. nov. and D. ocomphalum sp. nov. in the nearly parallel flanks, which are convergent in the other two species. Furthermore, D. myloide has a broadly rounded venter and a rounded ventrolateral shoulder, while the other two species have an applanate or even slightly concave venter and an angular ventrolateral shoulder.

Domatoceras myloide sp. nov. differs from D. elegantulum and D. multituberculatum from Julfa in the nearly parallel flanks, which are convergent in the other two species. Domatoceras parallelum has parallel flanks, but according to the description and illustration by Abich (1878: 17, pl. 2 fig. 2), it has a much wider umbilicus (uw/dm ~ 0.45) than D. myloide (uw/dm ~0.35).