86 THE NAUTILUS. 
NOTES ON NEW SPECIES OF AMNICOLIDZ COLLECTED BY DR. RUSH 
IN URUGUAY. 
BY H. A. PILSBRY. | 
Full descriptions of the new forms collected by Dr. Rush will 
appear as soon as illustrations can be prepared. Meantime, the 
following notes on the Amnicoline species may be of service. 
The South American fresh water Hydrobioids fall into three or 
four genera: PoraMoPpyRGus Stimpson, apparently confined to the 
extreme northern border of the continent, and perhaps to be re- 
garded as astraggler from the Antillean and Middle American 
fauna. Lirrortptna Eydoux & Souleyet, a characteristic South 
American genus of slender, acute shells, usually called “ Paludes- 
trina,” “ Hydrobia” or Heleobia Stimp. LLyropes Doering, possi- 
bly a group subordinate to Potamopyrgus. LirHoGLypHus of 
authors, stout of figure, thick and strong, the American forms 
with the lip expanded or having an external varix, or contracted 
by a callous deposit within the posterior angle in fully adult exam- 
ples. These seem to me to differ conchologically from the Euro- 
pean types sufficiently to call for generic distinction, and the new 
term 
PoTAMOLITHUS 
may be applied to them. Type P. Rushii. 
The genus Cochliopa Stimpson, with two Central American spe- 
cies, C. Rowelli Tryon and C. Tryoniana Pils., is like Potamolithus in 
the solidity of the shell, but it is heliciform and umbilicated. Lacu- 
nopsis and Jullienia, two Cambodian genera, are evidently near akin 
to the South American Potamolithus (see Journ. de Conchyl. 1881, 
p. 4). 
The peculiarly striking modifications of the species of this genus 
are scarcely paralleled in recent fresh water prosobranchs outside of 
Lakes Tanganyika or Baikal. They cannot well be appreciated 
without the aid of figures, which the writer intends publishing as 
soon as practicable. Until then, the species may be discriminated 
by the following diagnoses, which for more ready reference have 
been cast into the form of a key. The characters of previously 
known species are much abridged. 
I. Columella with a longitudinal groove or pit; outer lip with a 
strong varix. 
