366 
PALAEONTOLOGY OF NEW YORK. 
The hinge of the right valve shows a thickened plate bearing a single 
angular fold just beneath the beak. Nothing is satisfactorily known about 
the muscular impressions. 
Four specimens measure respectively 31, 57, 65 and 93 mm. in length, and 
23, 36, 46 and 63 mm. in height. 
This species more nearly resembles G. circular is than any other form of the 
Hamilton and Chemung groups, but it is usually more elliptical in outline and 
the umbonal ridge is stronger and more distinctly defined. In G. elliptica the 
cincture is usually well defined, while in G. circularis it is obscure or obsolescent. 
The specimen illustrated in figs. 5 and 6 of plate lviii has the form of G. 
circularis. The cincture is exaggerated in figure 5, being very obscure in the 
specimen. 
Formation and localities. In the Chemung group, at Philipsburgh, Alleghany 
county; near Ithaca, Tompkins county, N. Y., and near Mansfield, Tioga 
county, Pa. 
b. obsoleta. 
Grammysia obsoleta. 
PLATE LIX, FIGS. 21-27. 
Grammysia obsoleta, Hall. Prelim. Notice Lamellibranchiata, 2, p. 60. 1870. ' 
“ “ “ Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 59, lig-s. 21-27. 1883. 
Shell large, general form broadly ovate, becoming elliptical and sub-rhomboidal 
from pressure; length more than one-third greater than the height; basal 
margin regularly rounded, frequently with a slight constriction near the mid¬ 
dle. Posterior extremity regularly rounded, curving into the basal margin 
without limitation. Cardinal line more than half the length of the shell, 
arcuate, declining toward the posterior extremity. Escutcheon distinctly 
limited. Anterior end short and abruptly rounded below the lunule. 
Valves regularly convex below and posteriorly, becoming gibbous in the 
middle and above. 
Beaks sub-anterior, large, elevated, with the apices strongly incurved. 
