MOIvLUSCA. 603 



1864. Dosinia excavata Meek, Check List Inv. Foss. N. A., 



Cret. and Jur., p. 13. 

 1866. Cyprimeria excavata Con., Am. Jour. Conch., vol. 2, p. 



102. 

 1868. Cyprimeria excavata-Con., Cook's Geol. N. J., p. 727. 

 1875. Cyprimeria alta Con., Kerr's Geol. N. Car., App. p. 27. 

 1886. Cyprimeria excavata Whitf., Pal. N. J., vol. i (Monog. 



U. S'. G. S., vol. 9), p. 159, pi. 22, figs. 16-17. 

 1886. Cyprimeria spissas Whitf., Pal. N. J., vol. i (Monog. U. 



S. G. S., vol. 9), p. 160, pi. 22, fig. 18. 

 1905. Cyprimeria excavata John., Proc. Acad. Nat. Sci. Phil. 



(1905), P- 15 



Description. — Shell, in the largest specimen observed, attain- 

 ing a height of 55 mm., and a length of 60 mm. The propor- 

 tions of height tO' length in ten individuals vary from i : i .08 to 

 I : 1.20. The average proportions of the ten individuals being 

 I : 1. 1 4- The varying proportions of height to length is in 

 no way correlated with the growth or size O'f the individuals. 

 The position of the beaks varies in the same ten individuals 

 from .32 to .47 of the length of the shell from the anterior ex- 

 tremity, the average position being .38+. 



The anterior margin oi the shell is broadly rounded, passing 

 intoi the rounded basal margin, posteriorly the margin is usually 

 obtusely subangular as it passes from the basal to> the posterior 

 region, the posterior margin being subtruncate below and di- 

 rected posteriorly backward from the posterior extremity of the 

 basal margin ; at about the middle of the height of the shell, above 

 the truncate region, the margin bends somewhat abruptly for- 

 ward and passes toi the beak in a long gentle curve, the curva- 

 ture somewhat increasing as it approaches the beak. In some 

 individuals the post cardinal slope is slightly humped towards 

 the beak by reason of a rather abrupt change in the curvature. 

 Behind the beaks the margins of the valves are strongly and 

 abruptly inflected to form a deeply excavated escutcheon. Valves 

 depressed convex, the left valve less convex than the right. 

 Beaks of the two valves nearly in contact, lunule obsolete. 



