Holopea, Hall, 1847

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 : 11

Holopea ? sp.

( Fig. 8 )

Material. Two specimens: ESKU-19- LP 2, 3.

Dimensions (mm): ESKU-19- LP 2: height = c. 3.8; width = 3.6. ESKU-19- LP 3: height = c. 6.3; width = 4.8.

Description. Turbiniform to naticiform, moderately high-spired shell consisting of three to four whorls (apex missing); whorls rapidly increasing strongly convex, rounded, embracing below periphery; whorl surface ornament- ed by prosocyrt, prosocline collabral ribs; ribs irregularly pace of unequal strength; suture impressed; base evenly convex; minutely phaneromphalous; aperture seemingly circular, columellar lip somewhat straight.

Remarks. These two incomplete specimens with deep suture, rounded whorls that bear collabral axial ribs resemble the Ordovician genus Holopea which has never been reported from the Permian of Thailand. However, similar shell morphologies have been reported frequently from Palaeozoic and Mesozoic strata and were assigned to various other genera. For instance, Coelostylina costata Batten & Stoke, 1986 , a putative representative of the basically Mesozoic genus Coelostylina from the Early Triassic of the U. S. is quite similar to our specimens. H. bacca Pan & Erwin, 2002 (p. 13, fig. 8.5–8.11) from the Permian of South China resembles the present specimens the most in general features. The coiling direction of the protoconch is important for species assignment and it is slightly oblique to the axis in H. bacca . The coiling direction of the protoconch in the studied specimens is poorly preserved, therefore the species treated in open nomenclature.

Figures

FIGURE 8. Holopea? sp., A–C, ESKU-19-LP 2. D–F, ESKU-19-LP 3. All scale bars represent 1 mm.