192 MOLLUSCA FROM THE CRAG. 



sides sulcated ; a sharp and angulated keel extends the whole length of the shell 

 on each side. 



Length, \ of an inch ; transverse diameter ', one line. 



Locality. Cor. Crag, Sutton. 



This species is at present rare, most likely from its extreme fragility. In all 

 probability the posterior extremity was closed and pointed, but in each of my 

 specimens it is open. The sharp and sheath-like termination is not cylindrical, but 

 compressed before and behind, leaving a carinated edge on each side, which is con- 

 tinued all the way up the shell. There is a sulciform depression on both sides of 

 the expanded part, before as well as behind ; those portions are not, however, of 

 equal magnitude. It was no doubt transparent in the recent state, although it 

 looks now like an opaque shell, and is not very thin. 



