this difference in the umbilicus renders the separation of the 
species a matter of comparative ease. 
The peculiar arrangement of the internal lamelle& char- 
acteristic of this species is only assumed at maturity. In 
immature specimens the arrangement is almost precisely the 
same as that of young zrgo. But they can easily be separ- 
ated by observing the difference in the Size of the umbilicus. 
Gude (Science Gossip, III p 126) has shown that the same 
peculiarity is to be found in the East Indian Corz//c. 
24. PUPOIDES MARGINATUS (Say). 
More commonly known as Pupa or Leucocheila fallax. 
Not a common species. Reported from Kent, Genessee 
and Washtenaw counties. also from Post-pleiocene deposits 
in Berrien county (Naut. XI p. 121). 
25. BIFIDARIA ARMIFERA (Say). 
The returns indicate a general distribution through the 
southern part of the state. ‘‘Scarcein Kent county,” Streng. 
26. BIFIDARIA CONTRACTA (Say). 
The most common species of the genus and of general 
distribution over the lower peninsula. 
~ 
27. BIFIDARIA CORTICARIA (Say). 
Saginaw-Grand valley in Kent, Saginaw and Gratiot 
counties. ‘*Rare in Kent county,” Streng. 
28. BIFIDARIA CURVIDENS (Gld. ) 
Not abundant, but apparently of general distribvtion 
through the state south of the Saginaw- Grand valley. ‘Rare 
in Kent county,” Streng. 
29. BIFIDARIA PENTODON (Say). 
Distribution similar to the preceding. Alsoin Newaygo 
and Charlevoix counties. ‘* Plenty in some localities in Kent 
county,” Streng. 
30. Pupa muscorum (L,) 
Kent county is the only reported locality for this species, 
where it is ‘‘rare” according to Streng. 
31. VERTIGO MILIUM (Gld.) 
Reported only from Kent, Oakland and Lenawee counties. 
“Rare in Kent county,” Streng. 
17 
