364 PALEONTOLOGY OF NEW YORK. 



GrAMMYSIA CIRCULARI8. 



PLATE LVII, FIU8. 3-« ; ANU I'l.ATE LVIII, VUi. 13. 



Qrannnysia circnlarU, Hall. Pi-elim. Notice Lamellibranchiata, 2, p. 51. 1870. 



" " " Pal. N. y., vol. V, i)t. 1. Plates and Explanatioii.s : PI. 57, figs. 3-G; pi. 58, 



fijf. 13. 18S3. 



Shell from medium to large size, sub-circular in outline, ventricose ; length 

 about one-fifth greater than the height; basal margin regularly rounded, 

 except a slight sinuosity posterior to the middle ; posterior margin regularly 

 rounded from the post-inferior extremity to the cardinal line. Cardinal line 

 short and arcuate. Anterior end short and narrow, regularly curving from 

 the lunule into the basal margin. 



Valves regularly convex along the lower portion, becoming gibbous and 

 ventricose above and in the umbonal region. 



Beaks sub-anterior, prominent and strongly incurved. The beak and 

 umbo marked by a cincture, consisting of a ridge and shallow furrows, which 

 becomes somewhat obsolete on the middle of the valve, but is continued to 

 the basal margin, marking the shell in its passage by an undulation in the 

 striae which produces a slight projection in the centre, with a shallow con- 

 striction posterior to it. These features alternate in the two valves. 



Surface marked by fine concentric striae, which become fasciculate toward 

 • the base and on the anterior end, forming distinct ridges or undulations of 

 the surface. No radiating striae have been observed. 



The hinge, as shown in tigs. 5 and 6 of plate Ivii, has a strongly marked 

 ligamentnl area extending half the length of the shell, and a well-defined 

 lunule. Figs. 3 .and 4 show the anterior muscular impression just within the 

 anterior border and encroaching upon the lunule. The pallial line continues 

 parallel to the basal margin, recurving abruptly and terminating in the large 

 posterior muscular scar on the post-cardinal slope. The course of the pallial 

 line, in the cast, is marked by regular, elongate, pustulose striae, extending 

 from above and terminating in that line. The interpallial area is marked by 

 numerous elongate pustules. 



Three specimens measure respectively 67, 70 and 87 mm. in length, and 



