36 



thicker ; 2. the Tvrhorla are lying in one plane, the spire is depressed, 

 not elevated, as with the other species; and the lašt ^vhorl .vhich 

 almost entirely forma the whole sheU. is very much drawn down ; 

 3 it is not perforated. and although largely umbilicated yet the 

 other smaUer ■whorls are not visible in the umbilic ; and 4, it distin- 

 euishes itself by a very callous columella. which partly propagates 

 over the spire, foUowing the suture at a distance of five hnes. 



