558 CRETACEOUS PALEONTOLOGY. 



Crassatellites prorus (Conrad). 



Plate LXL, Pigs. 6-7. 



1869. Crassatella prora Con., Am. Jour. Conch., vol. 5, p. 43, 



pi. I, %. 8. 

 1876. Btea prora Con., Proc. Acad. Nat. Sci. Phil. (1876), p. 



275- 

 1886. Crassatella prora Whitf., Pal. N. J., vol. i (Monog. U. 



S. G. S., vol. 9), p. 120, pi. 17, figs. lo-ii. 

 1905. Crassatellites prorus Johns., Proc. Acad. Nat. Sci. Phil. 

 (1905), P- 14- 



Description. — "Shell below a medium size, transversely sub- 

 elliptical when considered exclusive of the projection of the 

 beaks, but transversely broad triangular if they are considered. 

 Valves rather ventricose for the genus; beaks very large, nearly 

 central or a little nearest the anterior end, strongly projecting, 

 and in the cast, the only condition in which it is known, nearly 

 erect and moderately distant. Posterior cardinal margin regu- 

 larly sloping from the beaks to. the narrowly rounded posterior 

 extremity ; anterior side of the beaks excavated and the anterior 

 end more broadly rounded than the opposite end; basal line 

 broadly curved. Umbonal ridge scarcely angular. Surface, as 

 shown on the casts, marked by comparatively strong, regular, 

 concentric ridges, and marked just anterior tO' the umbonal angle 

 by a proportionally broad sulcation passing from near the beaks 

 to the base. Muscular scars distinct." (Whitfield.) 



The dimensions of the type specimen are: length, 22.5 mm.; 

 height, 15 mm.; thickness, 10 mm. 



Remarks. — This species has been only rarely met with in the 

 recent collections of the Survey. It is of a rather exceptional form 

 for species of this genus, in its subelliptical outhne and its nearly 

 central beaks. It is quite different in all its characters soi far as 

 they are preserved, from typical members of the genus Btea 

 where Conrad has referred it, although the hinge characters 

 have not been observed. It seems better, therefore, to allow it 

 to remain in the genus where it was originally placed, than to 

 transfer it to' another. 



