TO GEOLOGY. 51 



ner, and in being more inflated. The dorsal margin is 

 but slightly curved. 



E. nitens. Plate 1. Fig. 19. 



Description. Shell subelliptical, obliquely transverse, 

 inequilateral, the anterior portion being much the larger, 

 rather compressed, smooth and shining ; substance of the 

 shell very thin ; posterior slope lightly folded ; beaks ele- 

 vated, pointed ; cicatrices scarcely perceptible ; cavity of 

 the shell not deep, of the beak rather deep ; margin entire. 



Diam. .1, Length 5-20ths, Breadth 6-20ths, of an inch. 



Observations. At first view this species might be taken 

 for the inftata. On examination it will be easily distin- 

 guished by its polish, its obliquity, and particularly by the 

 great disparity of the size of the anterior portion of the 

 shell, the inflata being nearly equilateral. 



E. triangulata. Plate 1. Fig. 20. 



Description. Shell triangular, inequilateral, smooth, ob- 

 tusely angular before, acutely angular at top, gibbous over 

 the umbo anterior to which it is flattened ; substance of 

 the shell rather thin ; posterior and anterior slopes flatten- 

 ed ; beaks elevated, pointed, incurved ; basal margin emar- 

 ginate ; cicatrices not perceptible ; cavity of the shell deep 

 in the superior part of the beak deep and angular ; in- 

 ferior portion of the margin finely crenulate. 



Diam Length .1, Breadth 1.2, inches. 



