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New Species or Fresh WATER Motuusk. 275 
acter which makes the young appear proportionately mu 
narrower than the adults; the anterior slope of the shell 
long and strongly convex, the posterior being short and 
_ concave. 
The surface is marked by fine lines of growth. The largest 
specimen which was secured has the following dimensions: 
length, 3.5 mm.; width, 1.8 mm.; height, 1.5 mm. The 
average dimensions are: length, 2.7 mm.; width, 1.7 mm.; 
height, 1.2 mm. The radula is rather narrow, the dental for- 
mula being 12-1-12. A rachidian tooth and one of the inner- 
most laterals will be figured on a plate in our next BULLETIN. 
The animal is of a uniform bluish-white color; the foot is 
ovate, wider anteriorly, and rather narrow for an Ancylus. 
This species occurs, not uncommonly, about five miles east 
of Lincoln, Neb., in Dead Man’s Run, a streamlet with 
numerous pond-like enlargements. Specimens were found by 
the author at all seasons of the year, adhering to shells of 
Anodonta plana, sticks, leaves, etc. Though diligent search 
has been made, no specimens have thus far been found in any 
_ other than the above-mentioned locality. 
The only other specimen of the genus which has been 
found by the author in the vicinity of Lincoln is A. r¢vudaris, 
Say, which is rather rare in Oak Creek, west of Lincoln. 
A more complete description and representation of the den- 
tition will be made in a subsequent issue of this BULLETIN, in 
a paper on the comparative dentition of the species of Azcylus. 
