TO GEOLOGY. 177 



my possession. Having been injured on a part of the 

 columella, it is impossible to decide on the number of its 

 folds, but presume it to be nine or ten. The front part of 

 the shell is coated somewhat like a Nassa. 



M. columba. Plate 6. Fig. 187. 



Description. Shell ovate, smooth ; substance of the 

 shell thick ; suture scarcely perceptible, spire somewhat 

 elevated, conical ; whorls , slightly convex ; colu- 

 mella with five folds ; mouth narrow, straight ; outer lip 

 much thickened, crenulate within. 

 Length 7-20ths, Breadth .2, of an inch. 



Observations. Like the last described, a single individual 

 only of this species came into my possession. In outline 

 they resemble each other. The columba has not, how- 

 ever, any deposit or coating it has a higher spire and a 

 less number of folds. The folds too are different in the 

 latter, having the appearance of being formed by the 

 grooving of the columella, while in the anatina they are 

 placed on the columella. 



M. crassilabra. Plate 6. Fig. 188. 



Description. Shell ovate, polished ; substance of the 

 shell thick ; spire very short, pointed ; whorls four, flatten- 

 ed above ; columella with four folds ; mouth narrow, 

 somewhat curved ; outer lip very thick, minutely crenu- 

 late within. 



Length 7-20ths, Breadth .2, of an inch. 



X 



