LOWER PERMIAN PERRINITID AMMONOID FAUNAS FROM THAILAND

Journal of Paleontology, Mar 2004 by Zhou, Zuren, Liengjarern, Malai

Material examined.-One internal mold (NlGP 135299) from mudstone, with septate phragmocone and partial body chamber.

Occurrence.-The E-Lert Formation, Artinskian Metaperrinites Zone; WCR.

Discussion.-The present specimen is identical with the type materials from Texas in conch form and suture details, representing the forms with the narrowest ventrolateral saddle in the genus. It also resembles Akmilleria adkinsi (Plummer and Scott, 1937) and A. huecoensis (Miller and Furnish, 1940) in conch form and general shape of suture, but its ventrolateral saddle is much narrower than those of the latter two species.

Genus BAMYANICERAS Termier and Termier, 1970

Propinacoceras KARPINSKY, 1890, p. 72 (part); HANIEL, 1915, p. 34 (part); TOUMANSKAYA, 1935, p. 74 (part); 1937, p. 108; 1949, p. 78 (part); 1963, p. 81 (part); MILLER AND FURNISH, 1940, p. 40 (part); TEICHERT, 1942, p. 224; RUZHENCEV, 1949, p. 114 (part); GLENISTER AND FURNISH, 1961, p. 690 (part); Artinskia ISHIBASHI, FUJIKAWA, AND NAKORNSRI, 1996, p. 190; Bamyaniceras TERMIER AND TERMIER, 1970, p. 94 (part); LEONOVA, 1984, p. 41; 1992, p. 131.

Type species.-Bamyaniceras bouyxi Termier and Termier, 1970, p. 94; original designation; Artinskian, Bamyan Mountains, Afghanistan.

Diagnosis.-Conch intermediate to large in size, platycone, involute, with widely flattened flanks; umbilicus very small; venter more or less flat, divided by a ventral furrow into two rows of wide nodelike elevations; suture characterized by definite subdivision in ventrolateral saddle: undivided ventral flank, two to four in crest and relatively large simple or bifid dorsal subdivision, and fairly large dorsal subdivision of primary external lateral lobe (L,^sub 1d^), usually greater than one-half size of adjacent primary umbilical lobe (U), both even subequal in extreme cases; sutural formula: (V^sub 2^V^sub 1^V^sub 2^)S^sup 1^S^sup 1^l^sup 1^L^sub 1(d)^^UU^sup 1^. . . .

Occurrence.-Eleven or more species; Lower Permian (Artinskian)-Middle Permian (Wordian); widespread in Pamirs, Afghanistan, Crimea, Sicily, Texas, Nevada, California, Timor, Western Australia, Guizhou, and Thailand (Loei).

Discussion.-Ventrolateral sutures of Bamyaniceras and Propinacoceras are fairly close, the dorsal subdivision of the ventrolateral saddle (l^sup 1^) in the former resembling in size and location the dorsal prong of the primary lateral lobe (L^sub 1(d)^) in the latter. Study of ontogeny reveals the fundamental difference.

BAMYANICERAS LOEIENSE

(Ishibashi, Fujikawa, and Nakornsri, 1996)

Figures 8.8-8.13, 9.1-9.3

Artinskia loeiense ISIIIBASHI, FUJIKAWA, AND NAKORNSRI, 1996, p. 190, pi. 13, figs. 1, 2, text-fig. 8.

Description.-Discoidal shell at least 55 mm in diameter with almost parallel flanks; umbilicus almost closed; venter bears two rows of prominent rounded nodes, which become transversely elongate and at full maturity develop into short ribs, nodes largely confined to venter and extend for only a very short distance on flanks; suture forms low and broad ventrolateral saddle, which is subdivided by an entire l^sup 1^ in dorsal side, a rounded s^sup 1^, and two shallow s^sup 1.1^ and s^sup 1.1^ in crest of ventrolateral saddle; primary lateral lobe (L^sub 1d^) asymmetrically bifid and greater than one-half size of adjacent primary umbilical lobe (U); bifid successive umbilically-derived lobes may appear at the first third to sixth lobes; whole auxiliary lobes may reach twelve or more on each side.