Neithea bexarensis (Stephenson, 1941)
STEPHENSON, L. W. 1941. The larger invertebrate fossils of the Navarro Group of Texas. University of Texas Publication, 4101: 1-641, pls. 1-95 [p. 136, pl. 22, figs. 7, 8]
1941 Pecten (Neithea) bexarensis Stephenson, 1941
1993 Neithea (Neithea) latericostata Muniz, 1993
1993 Neithea (Neithea) latericostata Muniz, 1993
L. W. Stephenson, 1941, plate 22.
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«Shell of moderate size, subcircular in outline, right valve strongly convex, greatest ventricosity central above the midheight, nearly equilateral, strongly inequivalve. Dorsal slopes steep, overhanging the ears. Beak of right valve prominent, strongly incurved, direct, slightly overhanging the beak of the left valve. The hinge line is straight and about 12 mm. long. The species belongs to a group of strongly inequivalve shells in which the right valve exhibits six major ribs with two or more smaller, subequal ribs in the interspaces between the larger ones. In this species there are two intermediate ribs, and the major ribs are only slightly more prominent than the intermediate ones. All the ribs are rather prominent, broadly rounded over the crests, and are wider than the interspaces. Each of the ribs is further ornamented with 2 to 5 subribs which are low and broadly roundcrested; these tend to become obscure and die out toward the beak. The interspaces are rather broadly rounded and are either without subribs or may have one or two very obscure subribs. The space between any two intermediate ribs is a little narrower than the spaces on either side of the major ribs. The space between the anterior major rib and the anterior ear presents one central narrow, shall subrib and back of this is a still smaller very obscure subrib. The space between the posterior major rib and the posterior ear presents 4 subribs and several intermediate very obscure subribs. The external interspaces are reflected on the inner surface of the shell as square-topped internal ribs, narrower than the interspaces; the subribs are only obscurely reflected internally. The anterior ear is of moderate size and is convex in a sinuous manner outward from the beak; it is separated from the main shell by a narrow, sinuous groove, and is ornamented with 7 or 8 small, narrow, unequal, radiating ribs. The posterior ear is subequal to the anterior one, and is similarly ornamented, except that on the holotype 4 of the centrally located ribs are so spaced as to form two pairs. The concentric markings consist of fine sharp, somewhat irregularly spaced ridges of submicroscopic size, numbering 5 to 10 to the millimeter. The left valve is not represented in the type material.
Dimensions of the holotype. a right valve: Length 23 mm., height 23.5 mm., convexity about 9 mm. This species has its nearest ally in Pecten (Neithea) austinensis (Kniker), from the Austin chalk at Austin, Texas, but differs mainly in that the two ribs between the major ribs are less closely crowded together; there is also a more obscure development of subribs in the bottoms of the interspaces. According to the measurements given for the Austin species, P. (Neithea) bexarensis appears to be more convex, and more nearly subcircular in outline. Types.— Holotype, U.S.N.M. no. 76444; 2 unfigured paratypes, U.S.N.M. no. 76445. Distribution in Texas.— Navarro group, Corsicana marl: 14 miles west by south of San Antonio (Tex. Bu. 742) ; 6 miles east of Castroville (15502, 16156, and Tex. Bu. 3282, type loc.) ; ?near Castroville (7665).» LLOYD WILLIAM STEPHENSON, 1941
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