192 MOLLUSCA FROM THE CRAG. 



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

 side. 



Lengih, \ 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 proba- 

 bility the posterior extremity was closed and pointed, but in each of my specimens it is 

 open. The sharp and sheath-like termination is not cyhndrical, but compressed before 

 and behind, leaving a carinated edge on each side, which is continued 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. 



