6o University of Michigan 



the last teeth present show that they are very near the outer 

 edge of the radula. 



These differences in the sculpture of the shell and in the 

 radula seem to warrant the separation of H. smnichrasti 

 Crosse and Fischer (1872) as the monotype of a new sub- 

 genus, Miraverellia. The descriptions of the shell-sculpture 

 and of the radula, given above, separate this group from Tri- 

 chodiscina von Martens (1892), of which H. coactiliata Ferus- 

 sac (1838) is the type. The radula of Averellia Ancey (1887), 

 in the strict sense (type H. macneili Crosse, 1873), has not 

 been examined, but this typical subgenus is separated distinctly 

 from either of the others by the peculiar, lamella-like infold- 

 ings of the last whorl ; the shell-sculpture is closer to that of 

 Trichodiscina. 



