Euomphalus cf. pronodocarinatus Pan & Yu, 1993

Ketwetsuriya, Chatchalerm, Karapunar, Baran, Charoentitirat, Thasinee & Nützel, Al- Exander, 2020, Middle Permian (Roadian) gastropods from the Khao Khad Formation, Central Thailand: Implications for palaeogeography of the Indochina Terrane, Zootaxa 4766 (1), pp. 1-47 : 10

Euomphalus cf. pronodocarinatus Pan & Yu, 1993

( Fig. 7 )

cf. Euomphalus pronodocarinatus Pan & Yu, 1993: p. 36 , pl. 2, fig. 4.

Material. Two specimens: ESKU-19- LP 61, 95.

Dimensions (mm): ESKU-19- LP 61: height = 1.7; width = 7.8. ESKU-19- LP 61: height = 2.0; width = 7.6.

Description. Small anisostrophic, discoidal shell; whorls rounded, convex, circular in transverse section, with the periphery at mid-whorl; whorls slowly increasing in diameter, only slightly embracing; suture deep; widely phaneromphalous with basal umbilicus deeper; whorl surface smooth with very faint and dense orthocline growth lines; rounded angulation on upper whorl surface at transition to upper umbilicus; base rounded; aperture subcircular, inner lip straight to somewhat concave.

Remarks. The present specimens closely resemble Euomphalus pronodocarinatus Pan & Yu, 1993 from the Lower Permian of Qixia Formation in Shangpingchuan, China in having a discoidal shape, a deep suture and numerous dense growth lines. However, the holotype of E. pronodocarinatus has nodes which are especially characteristic for this species that are absent in the studied material. Straparollus (Straparollus) planorbiformis de Koninck, 1881 as illustrated by Batten (1966 a, p. 15, pl. 2, figs 12–14) from the Lower Carboniferous of the Hotwells Limestone, England is also similar in having rounded whorls with well-developed growth lines but it differs in being more high spired. Another similar species is S. (Leptomphalus) micidus Yochelson, 1956 (p. 220, pl. 12, figs 1–4) from the Middle Permian of Southwestern USA which is discoidal and has a weaker upper angulation. However, S. (L.) micidus differs in having a sinus on the angulation of the upper whorl surface. There are other Permian euomphalid species which were reported from Southeast Asia such as Discotropis sp. from the Tak Fa Limestone of Thailand ( Ketwetsuriya et al. 2016), S. ( Euomphalus ) sp. from Perak, Malaysia ( Batten 1972), E. khmerianus Mansuy, 1912 from the Sisophon limestone of Cambodia ( Mansuy 1912; Delpey 1941) and E. subcircularis Mansuy, 1912 (pl. 7, figs 7–8). In addition, the present species also resembles S. (E.) alaskensis Yochelson & Dutro, 1960 from the Permian Siksikpuk Formation, USA, but the present specimens lack an upper angulation on whorl and the former species is larger in size. The studied specimens might represent a new species of the genus Euomphalus but the present material too poorly preserved to characterize it sufficiently.

Figures

FIGURE 7. Euomphalus cf. pronodocarinatus Pan & Yu, 1993, A–D, ESKU-19-LP 61. E–H, ESKU-19-LP 95. All scale bars represent 2 mm.