OF THE UNITED STATES. 55 



upper valve small in proportion to the lower, and marked with 

 distinct, concentric, squamous plates. 



Length, from one to two or three inches. 



Occurs chiefly in the arenaceous strata at Egypt, New 

 Jersey ; many individuals usually adhering by the beaks. 

 It is also found in the calcareous beds. 



The shell figured in the Journ. Acad. Nat. Sciences, 

 vol. vi. pi. v, fi^. 1, 2 and 3, under the name of G. vomer, 

 is a variety of G. convexa, and was introduced there by 

 mistake. 



The G. vomer is one of the most characteristic fossils 

 of the American cretaceous strata, occurring abundantly 

 both in the calcareous and arenaceous beds. 



4. G. Pitcheri, (S. G. M.) PL xv, fig. 9. 



Specific character. Shell thick, expanded, distinctly lobed ; 

 lower valve very convex; upper valve thick and sub-convex; 

 beak distinctly incurved. 



Length, one inch ; but I possess less perfect specimens 

 nearly three inches long. 



I received this fossil, together with some others of great 

 interest, from my friend Z. Pitcher, M. D., of the U. 

 States' army, who obtained it from the plains of the Kia- 

 mesha, in Arkansas. I have seen others from the falls of 

 Verdigris river, in the same territory. 



The G. plicatella, published by me in the American 

 Journal of Science, proves to be a variety of G. vomer. 



Exogyra, Say. 



E. costata, (Say.) PI. vi, ^. 1, 2, 3, 4. 



Amer. Journ. Science and Arts, vol. ii, p. 43. 

 Specific character. Sub-oval, thick; lower valve convex, 



