378 PALEONTOLOGY OF NEW YORK. 



Valves moderately convex, below and posteriorly, becoming gibbous above 

 the middle. 



Beaks sub-anterior, prominent, closely incurved and rising above the 

 hinge-line. Umbonal slope rounded, prominent near the beaks, but grad- 

 ually merging into the general convexity about the middle of the length 

 of the shell. There is a distinct cincture extending a little backward from 

 the beaks to the basal margin. 



Surfivce marked by fine concentric stria3, and extremely fine, pustulose, 

 nidiating striae; also by strong concentric undulations, which are sometimes 

 duplicate or intercalate near the anterior end and rarely in the middle of 

 their length, becoming obsolete before reaching, or upon, the post-cardinal 

 slope. The undulations are often a little deflected on the line of the cincture. 



Ligamental area distinct and elongate. Characters of the interior unknown. 



One specimen has a length of 40 mm. and a height from beak to base of 22 

 mm. A smaller individual has a length of 20 mm. and a height of 13 mm. 



This species is easily distinguished from any in the Hamilton group by the 

 strong, nearly vertical, mesial cincture and elongate form. 



The cincture in G. subarcuata is much farther anterior than in this species. 



From G. communis it is distinguished by the greater distance of the beaks 

 from the anterior end ; by its narrower posterior extremity, and by the more 

 nearly vertical direction of the mesial cincture. 



Formation and localities. In the arenaceous beds of the Hamilton group, near 

 Fultonham, and other parts of Schoharie county, and in the soft shales of the 

 formation on the shores of Seneca and Canandaigua lakes, N. Y. 



Grammysia communis, n. sp. 



PLATE LXI, FIGS. 84-28 ; AND I'LATE XCUI, FIG. 20. 



In part Grammysia ffannibalensis, (Shdhard), Hall. Pi-elim. Notice Lamellibranchiata, 2, p. 62. 1870. 

 " Orammys'w. {Leptodumust) Hannibalensis, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explana- 

 tions: PI. 61, figs. 23-33. 1883. 

 Not Allorimna Haunibaleniiu, Shdmard. Gleol. Surv. Missouri, Rep., pt. ii, p. 206, pi. C, tig 19. 185.'). 



Shell small, ovate-cuneate ; length less than twice the height ; basal margin 

 gently curving with a slight constriction just anterior to the middle of the 



