TO GEOLOGY. 201 



above and below ; substance of the shell thin ; spire um- 

 bilicate ; whorls compressed above ; columella twisted 

 and reflected at the base ; mouth linear, curved, extending 

 above the spire ; outer lip sharp. 

 Length 7-20ths, Breadth 3-20ths, of an inch. 



Observations. This species might at first view be taken 

 for the St Hillairii, but may, on examination, be readily 

 distinguished by its conical top. I have found it much 

 rarer in this deposit, having been able to obtain but three 

 specimens, while the other exists in great numbers. It is 

 not cylindrical, like that species, but rather disposed to be 

 conical above. They also differ in the base. 



Marginella biplicata. Plate 6. Fig. 216. 



Description. Shell pyramidal, transversely striate, 

 emarginate at base ; substance of the shell thick ; spire 

 elevated, pointed ; whorls four, rounded ; columella with 

 two large folds ; mouth small ; outer lip very thick and 

 minutely crenulate within. 



Length over .1, Breadth .J, of an inch. 



The smaller figure is of the size of nature. 



Observations. On the superior part of the whorl the 

 absence of a stria makes rather a broad band, above which 

 is a single stria only. This is near the suture, and on the 

 superior whorls it is the only one visible. With a good 

 deal of hesitation I have placed this minute shell with the 

 Marginella. Its elevated spire and emarginate base 

 would seem almost to forbid its being placed with them. 

 2 A 



