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. pl. v, fig. 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. e 
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. 
Exoeyra, Say. 
E. costata, (Say.) PI. vi, fig. 1, 2, 3, 4. 
Amer. Journ. Science and Arts, vol. ii, p. 43. 
Specific character. Sub-oval, thick; lower valve convex, 
