366 PALMONTOLOGY OF NEW YORK. 



The hinge of the right valve shows a thickened phite 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. circularis 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 Iviii 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. 



Oraiamysia obsoleta. Hall. Prelim. Notice Lamellibranchiata, 2, ju 60. 1870. ' 



" " " Pal. N. Y., vol. V, pt. 1. Plates and Explanations : PI. 59, tigs. 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. 



