OF THE UNITED STATES. 57 



Pecten 



1. P. quinquecostatus, (Sovverby.) 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 Sow T erby and 

 Brongniart. The last named naturalist makes the follow- 

 ing remark on this species : — " Ce peigne qui parait pre- 

 sents des varietes asses nombreuses de dimensions, et 

 meme 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 Chama halioloidea and C. conica, which I had 

 indicated as belonging to Mr. Say's genus. 



Mr. Sowerby suggests that the Exogyra 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 Gryph^ea 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, pi. iii, fig. 5. ■» 



H 



