Bellerophon erawanensis, Ketwetsuriya & Karapunar & Charoentitirat & Nützel, 2020

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 : 8-9

Bellerophon erawanensis sp. nov.

( Fig. 6 A–G)

Etymology. After the Erawan Hill at which the studied gastropod material was found. Holotype. ESKU-19-LP 55 .

Paratypes. Three specimens, ESKU-19-LP 54, 56, 59.

Dimensions (mm): ESKU-19-LP 59: height = c. 11.7; width = 13.1; thickness = 10.6. ESKU-19-LP 55: height = 9.9; width = 8.1; thickness = 8.0. ESKU-19-LP 54: height = 9.5; width = c. 9.4; thickness = 7.1.

Type locality and stratigraphical range. Erawan Hill, Chong Sarika sub-district, Phatthana Nikhom district, located about 13 km east of Lopburi Province, Central Thailand ( Fig. 1 ), Khao Khad Formation, Saraburi Group, Middle Permian, Roadian.

Description. Bellerophontiform, subglobular and slightly compressed shell, higher than wide; anomphalous, umbilical region covered by distinct callus; dorsum evenly rounded; whorls with a distinct slit; slit narrow and rather shallow; whorls covered by numerous closely arranged strengthened growth lines forming almost ribs, growth lines slightly curved backwards towards selenizone at an angle of about 70 degrees; inductura thin, ornamented with several growth lines developed continuing from whorl face; selenizone at periphery, narrow (c. 0.3 mm wide), marked by short curved transverse lunulae, at almost the same distance as of growth lines; aperture reniform in transverse section, tiny V-shaped indentation at crest; lateral lip arched, somewhat angulated after wing-like turnout of lateral lips and smoothly joining anterior lips; outer lip sickle-shaped as suggested by course of growth lines.

Remarks. Bellerophon has previously been reported from the Middle Permian of Thailand ( Ketwetsuriya et al. 2016, 2020) but it has been treated in open nomenclature because the preservation of that material is too poor for identification. Bellerophon erawanensis sp. nov. closely resembles B. jonesianus de Koninck, 1863 from the Permian of Pakistan (Chideru), which was also reported from the Permian of Pakistan (Salt Range) by Waagen (1880) and from the Permian of Japan (Akasaka Limestone) by Nützel & Nakazawa (2012). Bellerophon jonesianus has a similar ornamentation of pronounced growth lines, a narrow slit and a slightly elevated selenizone. However, B. erawanensis sp. nov. differs from B. jonesianus in having a less inflated shell, a narrower selenizone, a considerably higher number of fine threads formed by strengthened growth lines.

B. (Bellerophon) sowerbyi? d’Orbigny, 1840 as illustrated by Rollins (1975) from the Lower Mississippian of Southeastern Iowa is similar but this species has stronger growth lines and a slightly narrower selenizone. B. (B.) kingorum Yochelson, 1960 from the Permian of the Southwestern USA is also similar but has a more globular shape, thicker inductura and deeper slit. B. (B.) huecoensis Yochelson, 1960 can be differentiated by a deeper slit, a much more elevated selenizone, reflexed lateral lips and a very large size.

Figures

FIGURE 6. A–G, Bellerophon erawanensis sp. nov. A–E, ESKU-19-LP 55, holotype; E, shell showing V-shaped slit at crest. F, ESKU-19-LP 54, paratype; shell showing growth lines and position of selenizone. G, ESKU-19-LP 56, paratype. H–J, Bellerophon sp. H–I, ESKU-19-LP 58. J, ESKU-19-LP 59, shell fragment showing growth lines and position of selenizone. All scale bars represent 2 mm.

FIGURE 1. Geological map of the study location at Erawan Hill, Chong Sarika sub-district, Phatthana Nikhom district, located about 13 km east of Lopburi Province, Central Thailand.