MOLLUSCA. 539 



1864. Venilia rhomboidea Meek, Check List Inv. Foss. N. A., 



Cret. and Jur., p. 13. 



1868. Venilia rhomboidea Con. /Cook's Geol. N. J., p. 727. 

 1886. Veniella rhomboidea Whitf., Pal. N. J., vol. i (Monog. 



U. S. G. S., vol. 9), p. 215, pi. 28, figs. 12-13. 

 1905. Veniella rhomboidea Johns., Proc. Acad. Nat. Sci. Phil. 



(1905), p. 14. 



Description. The dimensions of a nearly perfect internal cast 

 are: length, 19 mm. ; height, 15 mm. ; thickness, 14 mm. Shell 

 trapezoidal or subrhomboidal in outline. The beaks situated near 

 the anterior margin, strongly incurved and directed forward. 

 Anterior margin short, sharply rounded; ventral margin nearly 

 straight, usually slightly convex anteriorly and straight or slightly 

 concave posteriorly; postero-basal extremity sharply angular; 

 posterior margin obliquely truncate, higher than the anterior 

 margin ; post-cardinal margin sloping gently backward from the 

 beak, slightly convex, becoming straighter posteriorly; posterior 

 cardinal extremity obtusely angular. Valves strongly ventricose 

 with a prominent, sharply angular, curved umbonal ridge; pos- 

 terior slope abrupt, concave, abruptly inflected to the cardinal 

 margin; anterior slope gently convex or nearly flat across the 

 middle of the shell, sometimes with a slight sinus towards the 

 ventral margin just in front of the umbonal ridge; anteriorly it 

 curves abruptly downward to the anterior margin, and is inflected 

 below the beaks. Surface of the casts marked by a few incon- 

 spicuous concentric lines of growth ; the muscular impressions 

 faint, the posterior ones scarcely or not at all distinguishable 

 upon the casts; at the dorsal margin of the anterior muscular 

 impression is a ridge-like thickening of the shell which, in the 

 casts, appears as a distinct groove or furrow crossing the hinge- 

 line just beneath and in front of the beaks. 



Remarks. This species has always been considered as a mem- 

 ber of the genus Veniella, and the shell does have a superficial 

 resemblance to members of that genus. The hinge-characters, 

 however, have not been observed, and without these the true 

 generic relations of the species cannot be determined. One pecu- 

 liar character of these casts which is certainly different from any 



