LAMELLIBRANCHIATA. 365 



55, 59 and 70 mm. in height. A specimen preserving both valves has a 

 length of 53 mm., height 42 mm., and a depth to both valves of 32 mm. 



This species is readily distinguished from any of its associated forms by its 

 sub-circular outline, in which character it seldom varies; and also in the absence 

 of a distinct cincture below the middle of the valve. 



Formations and localities. In the Hamilton group, in Albany, Schoharie and 

 Madison counties; in the Chemung group, at Nichols, in Tioga county, Cort- 

 land, Cortland county, and Ithaca, Tompkins county, N. Y. 



Grammysia elliptica. 



PLATE LVllI, FIGS. 1-12 (1, 6, 6?). 



Oramiaysia elliptica. Hall. Pi-elim. Notice Lamellibranchiata, 2, p. 53. 1870. 



" Pal. N. Y., vol. V, pt. 1. Plates and Explanations: PI. ."58, figs. 1-1-2. 18S3. 



Shell of medium or large size, transversely elliptical ; length varying from 

 one-sixth to one-third greater than the height ; basal margin broadly curving, 

 slightly sinuate about the middle ; posterior margin abruptly rounded below 

 and curving into the cardinal line above, sometimes more or less truncate. 

 Cardinal line arcuate. Anterior end narrow and abruptly rounded below 

 the lunule. 



Valves regularly convex below, becoming more or less gibbous above the 

 middle and in the umbonal region. 



Beaks sub-anterior, very prominent, strongly incurved, rising considerably 

 above the hinge-line. Umbonal slope rounded, arcuate. Cincture consist- 

 ing of a fold and furrow, extending downward in a curving direction to 

 the base of the shell, producing a gentle sinuosity in the basal margin. The 

 fold is more strongly developed in the left valve and the furrow in the 



right one. 



Test thick, marked on the posterior and middle portions of the shell by 

 fine, irregular, concentric striae, which become aggregated into fascicles on the 

 middle of the shell ; and on the anterior part marked by strong concentric 

 undulations. No radiating striae have been observed. 

 47 



