CRETACEOUS FOSSILS. 187 



CARDIUM, Linn. 



C. (L^BVICARDIUM) ANNULATTJM, Gabb. 



PI. 30, Fig. 81. 

 (C. (LcEvicardium) annulatum, Gabb; Pal. Cal., Vol. 1, p. 171, pi. 23, fig. 152.) 



This beautiful and delicate shell was described and figured from a distorted speci 

 men. Since the publication of Volume 1, numerous specimens have been obtained 

 by Mr. Mathewson at Martinez, and I am enabled to correct a point in the descrip 

 tion, and to give a more accurate figure of its form. The posterior side, instead 

 of being regularly convex, is slightly truncated obliquely. 



It is characteristic of the Chico Group, and seems peculiar to a series of bard 

 beds of this group found at Martinez, south of Mount Diablo, and in Orestimba 

 Canon, in the same range, further south. 



C. (PROTOCARDIUM) TRANSLUCIDUM, n. s. 



PI. 30, Fig. 82, 82 a. 



SHELL small, thin, gibbous, rounded subquadrate; beaks prom 

 inent, incurved; ends nearly equal, the anterior rounded, poste 

 rior rounded subtruncate ; base broadly rounded, a little more 

 prominent in advance than behind. Surface marked by a few 

 small, regular, rounded, radiating ribs on the posterior side, and 

 by concentric lines of growth. 



Length, .3 inch ; width, .3 inch ; diameter, .23 inch. 



From the same bed as the preceding, Martinez. 



Resembling C. (P.) Placerensis, this shell differs in its outline, being more quad 

 rate, in the posterior radiating ribs being more regular and numerous, and in the 

 entire absence of the large rib on the margin of the costate area, the marginal 

 rib in this species differing in no respect from the others. 



CARDITA, Brug. 



C. HORNII, Gabb. 



PI. 30, Fig. 83, a. 



(Cardita Hornii, Gabb; Pal. Cal., Vol. 1, p. 174, pi. 24, fig. 157.) 



(Cardita pianicosta, Con. (not Lam.) ; P. R, R. Rep., Vol. 6, p. 321, pi. 2, fig. 6.) 



