Radulonectites sosneadoensis (Weaver, 1931)
WEAVER, C. E. 1931. Paleontology of the Jurassic and Cretaceous of West Central Argentina. Memoirs of the University of Washington, 1: 1-469, pls. 1-62 [p. 272, pl. 28, fig. 169]
1931 Pecten sosneadoensis Weaver, 1931
W. C. Weaver, 1931, plate 28.
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«Description. Shell of medium size, moderately convex, sub-circular in outline with a large number of fine, but broad, flat-topped radiating ribs. The length of the shell nearly equals the height, and the hinge line is about one-half of the length. The anterior ear is about one-third larger than the posterior, and the apical angle averages 105°. The upper portions of the anterior and posterior margins are straight and form sub-angular junctions with tIle lower portions, which in turn gradually curve into the semi-circular basal margin. The surface of the left valve is ornamented with 70 fine, flat-topped, slightly sinuous, radiating ribs with interspaces ranging from one-fifth to one-tenth of their width. On the anterior end of the shell the ribs are somewhat narrower than on the middle and posterior ends. The radiating costae are crossed by unequally spaced lines of growth, as well as numerous very fine growth striae. The latter, upon crossing the interspaces, especially on the anterior end of the left valve, form microscopic, transverse, elongate grooves. The anterior ear is decorated with 10 radiating ribs, which are crossed by very strong lines of growth. The posterior ear possesses 6 radial costae, which are also crossed by very heavy growth lines.
Dimensions. Length, 26.5 mm; height, 27 mm; apical angle, 102°. Remarks. This species is characterized by the semicircular outline of the lower half of the valves, the triangular outline of the upper half, and the large number of fine, flat-topped radiating ribs with extremely narrow interspaces. The writer has been unable to find any form described in the literature of the Jurassic answering all of these characteristics, and accordingly the species is described as new. The species somewhat resembles P. (Chlamys) torulosa Quenstedt as figured in the monograph on Die Pectiniden des Schwaebischen Jura by Staesche (365), p. 33, pl. 1, fig. 1, but the ribs in his form are fewer in number, narrow and with much wider interspaces. Occurrence. Pecten sosneadoensis occurs in Mendoza at Sosneado at locality 1136 in association with Pecten disciformis Schuebler, and Trigonia inexpectata Jaworski in strata of the Lias. Type Material. Holotype. No. 153.» CHARLES EDWIN WEAVER, 1931
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