LAMELLEBEANGHIATA OF THE LOWEE MAELS. 159 



Cyprimeria excavata. 



Plate XXII, Figs. 16 and 17. 



Gytlierea excavata Morton. Synopsis, p. 67, PI. V, Fig. 1. 



Dosinia excavata (Mort.) Gabb. Synopsis, p. 120. Meek, Checklist, p. 13. Conrad, 



P. A. N. Sci. Phil., Vol. VI, p. 320. 

 1). densata Conrad. J. A. N. Sci. Phil., 2d ser.. Vol. in, p. 325, PI. XXXIV, 



Fig. 13 {=Cyprimeria alta Con. Kerr's Geol. X. C, Appendix, p. 27.) 

 Xot Dosinia donata (Con.) Meek (by error for D. densata). Geol. Surv. X. J., 1868, 



p. 727. 

 Cyprimeria excavata (Morton) Conrad. Am. Jour. Conch., Vol. II, p. 102. Meek, Geol. 



Surv. X. J., 1868, p. 727. 



Shell, as shown by internal casts, of medium size, transversely or trian- 

 gularly subcircular in outline, with distinctly unequal valves, the right 

 being prominently convex on the umbone and the left depressed convex, 

 becoming concave toward the front from the twisting of the valves, and 

 marked along the posterior slope by a faint plicature or depressed sidcus. 

 Beak small and appressed, curved anteriorly and subcentrally situated, the 

 anterior side somewhat excavated or concave, cardinal margin arcuate, and 

 the borders of the valves generally curved. Surface of the shell, as far as 

 can be judged from the casts, marked by concentric lines. 



The casts which I have referred to this species are more circular than 

 those pertaining to A. densata Conrad, and of smaller size and decidedly 

 shorter, with more erect beaks, and apparently more unequally convex 

 valves, which show no evidence of the distinctly flattened postero-cardinal 

 slope. No evidence of hinge characters remain on any of the few speci- 

 mens which I have examined, but the unequal valves, together with the 

 apparent bending or twisting of the basal portions, would seem to place 

 them at once among this group of shells. From their highly imperfect 

 conditions, however, no satisfactory proof of generic relations can be ob- 

 tained. Dr. Morton's figure is much more triangular in outline than any 

 specimen which I have seen. It is probable that he intended to include 

 under his species all those from the New Jersey Cretaceous now known 

 under the several names used. His description is, however, so very vague, 

 that it is impossible from it to decide which of these forms he had under 

 consideration. So we must depend entirely on his figure, which is but 

 little more satisfactory than the description. I have therefore retained for 



