TO GEOLOGY. 105 



is not perfect, is the only one which I have seen. It has 

 a short spire, but is most remarkable for its small and 

 almost round mouth, above which the margin is so much 

 thickened as to fill up a large portion of the arch. It is 

 more nearly allied to the guttula, than any other of the 

 genus. 



FAMILY NERITACEA. 



GENUS NATICA. Drapernaud. 



JV. striata. Plate 4. Fig. 88. 



Description. Shell obliquely elliptical, transversely and 

 closely striate ; substance of the shell rather thick ; spire 

 rather pointed ; columella smooth and thickened ; outer 

 lip sharp ; umbilicus small ; whorls four, depressed above, 

 rounded below ; mouth spread out, ovate, being two thirds 

 the length of the shell. 



Length .7, Breadth .5, of an inch. 



Sigaretus bilix ? Conrad. 



Observations. This interesting species approaches in 

 form the genera Stomatella and Sigaretus*, but is not suf- 

 ficiently depressed, to be placed with either of them. It 

 is disposed to be, like them, obliquely flattened in front. I 



* M. de Blainville says it is evident that the Sigaretus and Stomatella 

 can only be separated by the interior nacre of the latter, which is pearly. 

 o 



