Indopecten amusiiformis Hudson & Jefferies 1961
HUDSON, R. G. S. & R. P. S. JEFFERIES. 1961. Upper Triassic Brachiopods and Lamellibranchs from Oman Peninsula, Arabia. Palaeontology, 4 (1): 1-41, pls. 1, 2, text-figs. 1-12. [p. 19, pl. 2, figs. 5-7]
1961 Indopecten amusiiformis Hudson & Jefferies 1961
R. G. S. Hudson & R. P. S. Jefferies, 1961, plate 2.
|
«Pecten sp. ind. aff. Massalongi Stoppani. Diener 1908a. p. 131. pI. 23, fig. 10.
Holotype, LL309 (Pl. 2, figs. 5-7). Dicerocardium Limestone. Asfal Formation. Description. Shell thin-shelled, right valve slightly more convex than left. Length 32 mm., height 36 mm., thickness 11 mm. Umbones median, projecting slightly above hingeline; apical angle about 100°. Outline of flak of shell (apart from ears) an almost regular pentagon but angles rounded (except umbo).
Left valve with six weak folds separated by five weak furrows. Near the umbo these folds are stronger than farther away and somewhat angular. The two median folds coincide with rounded obtuse angles in ventral margin. Three median folds near umbo have weak secondary ribs which quickly die out ventrally. Indopecten structure present over whole valve. Ears separated from flank by elongate, concave areas, roughly perpendicular to commissural plane. Anterior margin of anterior ear arcuate with distinct byssal sinus. Posterior margin of posterior ear probably sinuous. Near ventral margin internal ribs present before and behind second to fifth radial folds. Internal ribs anterior and posterior to this possibly present but not seen. Right valve with five radial folds, very weak except near umbo. Folds separated by four furrows that are distinctly angular in section near umbo but much weaker ventrally. Internal ribs present near ventral margin in pairs before and behind each furrow with the addition of a single rib before the anterior radial fold. Ears separated from flank by sharp flexure. Anterior margin of anterior ear with distinct byssal notch. Posterior margin of posterior ear sinuous. Remarks. The hololype of I. amusiiformis clearly belongs to the same species as the specimen from the Monotis beds of Spiti described by Diener (1908a) as Pecten sp. ind. aff. massalongi. This specimen, contrary to Diener's opinion, is a left valve for his figure shows excellent Indopecten structure. I. amusiiformis not very similar to P. massalongi Stoppani in which the internal ribs are much more numerous. The new species differs from I. clignetti asperior (subsp. nov.) and I. clignetti clignetti (Krumbeck) in being more nearly equivalve, in having weaker secondary ribs, a thinner shell, and no crenulations on the radial folds of either valve. It dilTers from I. krumbecki (Jaworski) in having much weaker radial folds and from I. verbeeki (Boettger), I. microglyptus (Boettger), and I. misolensis (Jaworski) in lacking crenulations on both valves. I. glabra Douglas (not Krurnbeck 1913) is a much bigger species. very inequivalve and with strong secondary ribs. Entolium cf. subdemissum Muenst. (Diener 1908a, p. 138. pl. 24. fig. 12) at first sight closely resembles the present species but shows no sign of radial folds or Indopecten structure. Of the species just mentioned the one closest to I. amusiiformis is probably I. microglyptus (Boettger).» ROBERT GEORGE SPENCER HUDSON & RICHARD PETER SPENCER JEFFERIES, 1961
|