1898.] NATURAL SCIENCES OF PHILADELPHIA. 487 



was taken by Dr. Sharp at Unalaska. It resembles M. Sharpii 

 closely in color, texture and sculpture, but differs from it in the 

 following particulars of form : Seen from above the whorls of M. 

 Sharpii increase in breadth very much more rapidly, the last be- 

 coming far broader near the aperture. The umbilical area in M. 

 vorticifera is broad and excavated, but the umbilicus proper is com- 

 paratively small, round and deep ; while in M. Sharpii the excavated 

 area is not only much larger, but the entire cavity is widely open to 

 its beginning. In M. vorticifera the columellar margin of the per- 

 istome is broadly concave along the margin of the "funnel," passing 

 into a subtriangular dilation above (well shown in the front view of 

 Dall's original figures), which impinges upon the circular umbilicus 

 and to a small extent vaults it over, as in many Helices. In M. 

 Sharpii the columellar margin is much more deeply excised, and its 

 continuation above forms a raised wall curving around the entirely 

 open and far wider umbilicus. 



Types are No. 70, 554 of the conchological collection of the Acad- 

 emy of Natural Sciences of Philadelphia. 



