CRETACEOUS FOSSILS. 267 



C. (G.) SABULOSUM, D. 8. 

 PL 36, Fig. 14 



SHELL convex, nearly equilateral, rounded, subquadrate; beaks 

 central, slightly pointed in advance; umbones very prominent ; 

 cardinal margins equally and very slightly sloping; anterior end 

 and base regularly convex ; posterior end rounded, subtruncate. 

 Surface marked by from twenty to thirty radiating ribs bearing 

 small, elongate tubercles; between these ribs are broad, flat, 

 interspaces, each one with two or three fine, linear ribs, minutely 

 granulate. 



Figure, natural size ; transverse diameter, 1.15 inch. 



C. (PROTOCARDIUM) GRANULIFERUM, n. s. 



PI. 36, Fig. 15. 



SHELL large, thin, subquadrate, subcompressed. Beaks central, 

 strongly pointed in advance, umbones moderate ; cardinal mar 

 gins sloping; base broadly and regularly rounded; anterior end 

 rounded, sometimes rounded subtruncate; posterior end obliquely 

 truncate. Surface marked by from fifteen to eighteen radiating 

 ribs, which occupy the posterior face to beyond the posterior basal 

 angle ; some of these ribs, those nearest the outer margin of the 

 shell, carry small granulations, irregularly disposed along their 

 length. The remainder of the surface is covered by irregular 

 lines of growth. 



Figure, natural size of an average specimen. One fine example before me 

 measures length and width each, 3 inches, diameter of two valves, 1.8 inch. A 

 small specimen, less than an inch in length, has the heaks much less prominent 

 than in the figure, the cardinal margins much more sloping, and the whole outline 

 below forming a regular curve. On comparing the specimens with the figures of 

 C. (P.) multistriatum,Shum., in Emory's Report, pi. 6, fig. 4 a-c, the present form 

 seems to be more truncated posteriorly, and I can detect no indications of the 

 granules on the radiating ribs either in the figures or in the descriptions of Conrad 

 or Shumard. By comparing with some very imperfect specimens of Shumard's 



