OF THE UNITED STATES. 57 
PECTEN. 
1. P. quinguecostatus, (Sowerby.) PI. xix. fig. 1. 
This fossil is beyond a doubt specifically identical with 
the one described by Sowerby, and so characteristic of 
the cretaceous strata of Europe. I first detected it from 
casts,* but am now in possession of several shells, which 
answer in every particular to the figures of Sowerby and 
Brongniart. The last named naturalist makes the follow- 
ing remark on this species :—*‘ Ce peigne qui parait pre- 
senté des varietés asses nombreuses de dimensions, et 
méme de proportions dans les dimensions, est une des co- 
quilles les plus constantes dans les terrains de craie infe- 
rieurs.”’ 
2. P. craticula, (S. G. M.) 
Specific character. Suborbicular, unequal, with about ten 
large, elevated, convex, longitudinally striated ribs, and a 
smaller one interposed between each pair. 
Length, about an inch and a half. 
Of this rare and remarkable species I have not seen an 
found in or below the chalk formation,) which he had originally placed under the 
genus Chama. Among these are Cuama haliotoidea and C. conica, which I had 
indicated as belonging to Mr. Say’s genus. 
Mr. Sowerby suggests that the Exocyra costata and E. haliotoidea may be 
identical. I have examined many specimens of each, and although they appear 
to be analogues, they are obviously distinct species. 
Mr. Sowerby also thinks the American GryPHma convexa to be the European 
G. globosa. In this opinion I have to differ from him, and am supported by Mr. 
Mantell, to whom I have sent numerous individuals of the American fossil. 
* American Journal of Science, vol. xviii, pl. iii, fig. 5. 
H 
