LAMELLIBRAN CHI A TA. 
251 
muscular impression on the post-umbonal slope. The interpallial area is 
finely pustulose. 
This variety was originally separated from L. macroptera by reason of its 
proportionally broader, shorter, and more gibbous form; the arcuation of the 
body of the left valve, and its expansion on the antero-basal margin. In a 
single example of the left valve, the radii are much stronger than usual in 
typical specimens of the other form, and the interstitial radii more strongly 
developed. These characters, and others upon which the species was originally 
founded, when compared with a large number of individuals of the genus, are 
represented with many modifications, and the specific distinction is here 
continued with much reservation. 
On comparing the typical specimen of Mr. Conrad’s L. macroptera , we find 
it proportionally shorter and wider than many specimens since referred to the 
same species; measuring 63 mm. in length and about 78 mm. in height, the 
left valve very gibbous and the body sub-arcuate; the proportions being very 
nearly the same as in L. curvata, represented in fig. 2, of plate xxviii. 
Formation and localities. This species occurs in the Hamilton group at 
Cazenovia and other places in Madison county, N. Y. 
