Apachella thailandensis sp. nov.

(Fig. 11)

Etymology. After the country of Thailand.

Holotype. ESKU-19-LP 62.

Paratypes. Four specimens: ESKU-19- LP 25, 60, 89, 100.

Dimensions (mm): ESKU-19- LP 25: height = c. 9.4; width = 5.5; apical angle = 75º. ESKU-19- LP 62: height = 8.5; width = 5.2; apical angle = 60º. ESKU-19- LP 60: height = c. 4.6; width = c. 4.6. ESKU-19- LP 89: height = c. 7.1; width = c. 4.1; apical angle = 66º. ESKU-19- LP 100: height = c. 6.5; width = c. 4.8.

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. Shell high-spired, consisting of 8 whorls, first whorl planispiral; first two teleoconch whorls smooth, rounded, third whorl ornamented with spiral threads; selenizone starts within the 4th whorl; suture slightly impressed; subsutural ramp slightly convex, ornamented with 3–4 spiral ribs that are ornamented with nodes; selenizone concave, ornamented with very faint lunulae, bordered by two straight spiral ribs; lower rib forms periphery; lower whorl face twice as wide as the upper whorl face; lower whorl face slightly convex, ornamented with one spiral rib just above suture, equal in strength to spiral rib bordering the lower edge of selenizone; lower whorl face further ornamented with two spiral threads between two spiral ribs; base convex, ornamented with several evenly spaced spiral ribs of same strength as ribs on lower whorl face; base convex, anomphalous; aperture unknown.

Remarks. Apachella thailandensis sp. nov. has a wider upper whorl face (above selenizone) than other species of Apachella . The ratio of the height of the upper and the lower whorl face of A. thailandensis sp. nov. is similar to that of A. alimillana (Girty, 1909) . However, the latter lacks spiral ribs on upper whorl face. A. powwowensis Batten, 1995 has a wider selenizone, a median spiral lira on its selenizone and only one spiral rib on its upper whorl face. A. franciscana (Chronic, 1952) differs by having two faint spiral ribs on the upper whorl face adjacent to the suture, more prominent ribs bordering the selenizone, a stepped whorl profile and a higher whorl expansion rate.