Middle Permian (Roadian) gastropods from the Khao Khad Formation, Central Thailand: Implications for palaeogeography of the Indochina Terrane Author Ketwetsuriya, Chatchalerm Author Karapunar, Baran Author Charoentitirat, Thasinee Author Nützel, Al- Exander text Zootaxa 2020 2020-04-17 4766 1 1 47 journal article 22833 10.11646/zootaxa.4766.1.1 ed4d1bf6-284a-4898-952a-58943d5a3026 1175-5334 3763907 urn:lsid:zoobank.org:pub:B1B5DA41-5035-4783-8D47-28857B6305AE Platyzona gradata sp. nov. ( Fig. 23 ) Etymology. From Latin gradata, because of the gradate spire. Holotype . Only one specimen : ESKU-19-LP 11 . Dimensions (mm): ESKU-19- LP 11: height = 11.6; width = 8.3; apical angle = c . 72 º . 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. Moderately high-spired, turbiniform shell consisting of 6 whorls (apex missing) with a step-like whorl profile; early teleoconch whorls (first three whorls) rounded, convex, with an ornament of faint spiral threads (maybe due to preservation); upper whorl surface of later whorls developing wide, steeply inclined ramp; ramp slightly convex to straight ornamented by c . 8 to 10 equally spaced spiral threads; selenizone wide and flat, approximately 0.8 mm wide, covering almost half of whorl height of body-whorl, situated below ramp; adapical border of ramp at about mid-whorl, forming also angulated border of ramp; outer whorl surface of selenizone almost straight, parallel to shell axis, bordered by two spiral threads followed by strong spiral cords; selenizone with curved transverse lunulae; adapical spiral rib forming periphery; abapical spiral somewhat above lower suture; whorls embracing somewhat below abapical spiral rib; suture distinctly impressed; base flatly convex with numerous evenly spaced spiral threads, shallowly phaneromphalous; aperture not well-preserved, seemingly with straight columellar lip. FIGURE 23. Platyzona gradata sp. nov. , A–F, ESKU-19-LP 11, holotype. Scale bars represent: 2 mm (A–B, E–F); 1 mm (C–D). Remarks. Platyzona is reported from Thailand for the first time. Several species of this genus have been reported from other Permian assemblages from Asia e.g., from Cambodia ( Mansuy 1913 a ; Delpey 1941 ), Perak , Malaysia ( Batten 1972 ), South China ( Pan & Erwin 2002 ) and from the Akasaka Limestone, Japan (Nützel & Nakazawa 2012 ). It has also been reported from the USA ( Batten 1989 ). The single specimen at hand resembles the paratype of Platyzona dongluoensis ( Pan & Yu, 1993 ) from the Upper Permian Changxing Formation of south China ( Pan & Yu 1993 , pl. 8, fig. 3a–c). However, the holotype of this species differs considerably from the paratype and from the present specimen in having a narrow selenizone at mid-whorl and in other characters ( Pan & Yu 1993 , pl. 8, fig. 2a–b). The paratype of P. dongluoensis represents the genus Platyzona but the holotype and hence the species itself does not, the species reported by Pan & Erwin (2002) as of P . dongluoensis from the Late Permian of China resembles the misidentified paratypes of this species and P . gradata sp. nov. and could be conspecific. P . nodohumerosa Batten, 1972 from the Permian of Malaysia resembles P. gradata sp. nov. but has a nodular ornament and distinct spiral cords or lirae on the selenizone. P . eulkaiensis ( Reed, 1927 ) as illustrated by Batten (1972) from the Permian of Malaysia and by Nützel & Nakazawa (2012) form the Permian of Japan is also similar but has a narrower selenizone that is lower on the whorls (just above the suture) and a weaker spiral ornament. Three Late Permian species from South China have been assigned to Platyzona by Pan & Erwin (2002) : P . pulchella Pan & Erwin, 2002 lacks spiral cords and has more pronounced growth-lines. P . nitella Pan & Erwin, 2002 is broader and has more pronounced lunulae. P . luculenta Pan & Erwin, 2002 is based on an early juvenile specimen (protoconch and 1.5 teleoconch whorls). In contrast to P . gradate sp. nov. , it has strong spiral cords on the earliest teleoconch and the selenizone is higher on the whorls. Four Permian species from SW USA have been assigned to Platyzona by Batten (1989) : P . rotunda Batten, 1989 is broader and has entirely rounded whorls. P . cancellata Batten, 1989 has a much narrower selenizone and a cancellate ornament. P . pagoda Batten, 1989 is more slender and has a concave selenizone and has entirely rounded whorls. P . anguispira Batten , has uncoiled whorls.