TO GEOLOGY. 67 
the first to collect and arrange systematically the shells of 
our country, he has formed one of the finest cabinets in it. 
C. subcrassa. Plate 2. Fig. 43. 
Description. Shell somewhat inflated, subtriangular, 
concentrically striate, thick about the region of the hinge ; 
substance of the shell thick ; beaks thick and elevated ; 
lunule cordate, indistinct ; teeth rather elevated and com- 
pressed ; excavation of the palleal impression rather small 
and roundish ; cavity of the shell deep and rounded ; mar- 
gin crenulate. 
Diam..... Length 1.1, Breadth 1.2, of an inch. 
Observations. This shell most resembles the trigoniata 
herein described. It is like that shell in outline, but is 
thicker, and differs also in having a crenulated margin. 
C. trigoniata. Plate 2. Fig. 44. 
Description. Shell somewhat inflated, triangular, con- 
centrically and minutely striate ; substance of the shell 
rather thick; beaks moderately elevated and recurved ; 
lunule long, elliptical ; teeth moderately large ; excavation 
of the palleal impression deep and rounded ; cavity of the 
shell deep, subangular ; margin entire. 
Diam. .6, Length .9, Breadth 1.1, of an inch. 
Observations. In outline the trigoniata resembles closely 
the subcrassa. It is, however, less thick in the substance 
of the shell, has much finer striz, and is entirely without 
crenulations on the margin. 
