THE TERTIARY FORMATIONS OF VIRGINIA. 375 



are readily distinguished, however, by the greater length and curva- 

 ture of the whole anterior margin, especially the portion along the 

 ligament; the hinge is broader and longer, and the teeth are less promi- 

 nent and more arcuated; the muscular impression, on the anterior 

 side, is further from the hinge ; and the whole valve is wider, flatter 

 and thinner. These differences, with the flatness of the costae, appear 

 to warrant us in regarding this shell as a distinct species from Veneri- 

 cardia planicosta. That shell also is found in the eocene of Virginia, 

 but usually not in the same bed with V. ascia. 



Cardium quadrans. Plate XXX., fig. 1. 



Specific character. — Shell subtrapeziform, oblique, inequilateral, 

 posteriorly much expanded, compressed anteriorly ; thin and fragile ; 

 longitudinally ribbed, costae about thirty-five, broad, depressed, and 

 slightly convex ; transverse striae somewhat coarse or squamose near 

 the margin. Umbones small, beaks incurved, lunule long; posterior 

 cardinal tooth small, and of nearly uniform breadth, posterior lateral 

 tooth large ; margin crenulated by distinct but not deep undulations. 

 Length, three inches seven-tenths; breadth, two inches eight-tenths. 



Locality, eastern Virginia, meiocene. 



Remarks. — Owing to the extremely friable state in which this fossil 

 is found, and to its being associated with C. magnum and C. laquea- 

 ^wm, its fragments have passed for these species; but its trapezoidal 

 form, and the great width and depression of the longitudinal costae, 

 show a strong contrast to the laqueatum, while, in addition, its less 

 size and less inflation prove it different from the magnum. 



The great expansion of the posterior slope into an almost auriculated 

 margin, is highly distinctive of it as a new species. 



Crassatella capri-cranium. Plate XXX., fig. 2. 



Specific character. — Shell ovate, oblong, compressed, sub-rostrate, 

 rather thin, with coarse, obtuse, transverse wrinkles, and fine transverse 

 striae ; a prominent sinus extends from the beak to the anterior ter- 

 mination of the inferior margin ; truncated anteriorly, at a right angle 



VI. — 4 T 



