Porcellia magninodosa Pan, 1985

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 : 12-13

Porcellia magninodosa Pan, 1985

( Fig. 9 )

Porcellia magninodosa Pan, 1985: p. 35 , pl. 2, fig. 10; Pan & Yu, 1993: 43, pl. 6, figs 1–4.

Material. Two specimens: ESKU-19- LP 91, 125, 126.

Dimensions (mm): ESKU-19- LP 91: height = 4.0; width = 11.7. ESKU-19- LP 125: height = 3.0; width = 7.4. ESKU-19- LP 126: height = 2.0; width = 9.4.

Description. Shell discoidal, pseudo-isostrophic, with 5 whorls; whorls well rounded; first whorl dextrally coiled, slightly elevated; later whorls planispirally coiled, expanding moderately; slit deep, extends one third of the whorl; selenizone narrow, concave, situated approximately at mid-whorl; selenizone bordered by two spiral lirae, representing periphery; upper and lower whorl face ornamented with c. 24 to 26 prominent, regularly spaced nodes or obliquely elongated (opisthocyrt) costae; suture deep and impressed; aperture subcircular.

Remarks. The present species is a typical representative of the genus Porcellia with its slightly elevated first whorls and nearly planispiral, dextrally coiled later whorls, with deep slit and very narrow selenizone. The present specimens closely resemble the type specimen of Porcellia magninodosa Pan, 1985 (p. 35, pl. 2, fig. 10) in shape, size and ornaments as well as those assigned to P. magninodosa by Pan & Yu (1993, p. 43, pl. 6, figs 1–4) from the Late Permian of the Changxing Formation, China. Other similar species are Porcellia paucituberculata Pan & Erwin, 2002 (p. 10, fig. 5.10–13) from the Permian of Guangxi and Yunnan Provinces, South China and P. nodosa Hall, 1859 . The latter was also reported from the Lower Permian Sisophon Formation, Cambodia ( Delpey 1941, p. 365, fig. 39). P. nodosa differs from P. magninodosa in having a rectangular whorl profile and fewer costae. In P. paucituberculata , the nodes and the interspaces are wider and it has fewer costae compared to P. magninodosa .

This is the first known occurrence of the genus Porcellia in Thailand and the earliest occurrence of P. magninodosa . Our report extends the range of the species to the Middle Permian and expands its geographical range to further south in the Palaeo-Tethys.

The Porcellia species that have been recorded from the North America (e.g., Thein & Nitecki 1974; Kues 1984) and Europe ( Haughton 1859; Batten 1966 a) are from the Carboniferous of Panthalassa and the western Palaeo- Tethys, respectively. The Porcellia species reported from Asia are from the Permian of the eastern Palaeo-Tethys, e.g., P. nodosa Hall, 1859 from Cambodia ( Delpey 1941), P. puzoidea Hayasaka, 1955 from Japan, P. lingshuiensis Pan, 1985 from China, P. magninodosa Pan, 1985 from China and Thailand and P. paucituberculata Pan & Erwin, 2002 from South China. Our report further fills the biogeographic gap between these Carboniferous and Permian occurrences.

Figures

FIGURE 9. Porcellia magninodosa Pan, 1985, A–B, ESKU-19-LP 91. C, ESKU-19-LP 126. D, ESKU-19-LP 125. All scale bars represent 2 mm.