PLANORBIS, 208 
17. PLANORBIS BICARINATUS, Say. 
Hald. Monog. p. 6, t. 1, figs. 1—6. 
Distributed throughout the entire country 
east of the Rocky Mountains, but commonest 
in the waters of the Eastern and Middle 
States. 
 Planorbis lautus, H. Adams, from New Or- 
leans, has never been figured, nor have I seen 
an authentic specimen, but, judging from the 
description, I think it probable that it is the 
young of this species. 
Planorbis antrosus, Conrad, I am _ also 
inclined to place in the synonymy of bicarina- 
tus. It has not been figured, and, if different, 
has not been included in any of the numerous 
collections sent to us by zealous explorers like 
Dr. E. R. Showalter, who have so thoroughly 
examined the waters of Alabama for Mol- 
lusca. Mr. Conrad himself has no recollection 
‘of his species, which he described over thirty 
years ago. 
(50) 
