THE NAUTILUS. 123 
A NEW PLANORBIS FROM ILLINOIS.* 
BY FRANK C. BAKER. 
While making a study of the larger Planorbis of the Big Ver- 
milion River, Illinois, for a paper on the distribution of the 
mollusks of that stream, it became apparent that two forms 
were included under ¢rivolvis which were quite separable. One 
of these is the large, wide form to which Say gave the name 
trivolvis. The other is a narrower form which the writer and 
others have been calling glabratus (see Baker, Cat. I]. Moll., 
p. 106) but which is not the true glabratus of Say, which, ac- 
cording to Walker (Synopsis, p. 99), does not range outside of 
the State of Florida. Say credited his origina] specimens to 
Charleston, 8. C. The new Illinois form may be characterized 
as follows: 
Planorbis pseudotrivolvis n. sp. 
Shell sinistral, whorls 5; body whorl rounded above and _ be- 
low, the inner whorls carinated on both spire and umbilical 
region; the spire whorls are very flat and slightly concave; the 
earlier whorls are coiled so that they form a union with the 
carina of the preceding whor! but the last whorl gradually 
divides from this line, leaving a V-shaped depression between 
the dorsal carina and the body whorl; this condition is uniform 
for the dozen or so specimens examined: the base or umbilical 
region exhibits three full whorls to the umbilicus; aperture 
somewhat lenticular, rounded above and below, sometimes a 
trifle expanded, and bordered with red; color of shell yellowish 
or corneous inclining to brown; surface notably shining. 
Height, 9; greatest diameter, 20.5; aperture height, 8; breadth, 
9mm. Holotype. 
Height, 9; greatest diameter, 19; aperture height, 8; breadth, 
9mm. Paratype, 5 whorls. 
Height, 6; greatest diameter, 11.5; aperture height, 5; breadth, 
5mm. Immature, 4 whorls. 
* Contribution from the Museum of Natural History, University of Illinois, 
No. 8. 
