202 PLANORBIS. 
B. SPECIES INHABITING THE ATLANTIC AND 
Mippie States. 
16. PLANORBIS TRIVOLVIS, Say. 
Plate 6, fig. 16. 
Hald. Monog. p. 13, t. 2, f. 4—7. 
P. trivolvis, var. fallax, Hald., p. 15, t. 3, figs. 1, 2, 3. 
As previously remarked under Pl. Binney, 
Mr. Say’s Pl. corpulentus is the same as the 
species now under consideration. In the 
waters of the Northern border States and in 
Canada, Pl. trivolvis sometimes attains a very 
large size and is furnished with a somewhat 
reflected lip. I have figured such a specimen 
(fig. 16), being a shell described by Mr. Whit- 
eaves as Pl. macrostomus. Until recently I 
considered Mr. Lea’s Pl. regularis distinct, but 
a close examination leads me to the conclu- 
sion that it is not entitled to specific rank 
apart from trivolvis. 
Pl. proboscideus, Potiez, ascribed to North 
America, and included by Binney in the syn- 
onymy of this species, is, I think, of very 
doubtful position, and I incline to believe it is 
not North American. 
(49) 
