SOMATOGYRUS. 61 
Ohio River and tributary streams; Wiscon- 
sin. 
This species is larger, and the spire is more 
conical and sutures more deeply impressed 
than in the aldilis. The whorls are more con- 
vex, and the umbilicus visible, although 
narrow. 
Melunia isogona, Say, is the same species, 
and Paludina pallida, Lea (my figure 11) is 
the young. 
3. SOMATOGYRUS DEPRESSUS, Tryon. 
Plate 17, fig. 12. 
Shell orbicular, sub-hyaline; whorls four, 
convex, the last large, equaling five-sixths the 
length of the entire shell; umbilicus narrow ; 
aperture semicircular, labrum appressed with- 
in; suture impressed. 
Alt. and diam. 4 mill. 
Mississippi River at Davenport, Iowa. 
Differs from S. subglobosus in being smaller, 
and in the narrower aperture, of which the 
(42) 
