86 THE NAUTILUS. 



NOTES ON NEW SPECIES OF AMNICOLID.E COLLECTED BY DR. RUSH 



IN URUGUAY. 



BY H. A. PILSBRY. 



Full descriptions of the new forms collected by Dr. Rush will 

 appear as soou 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: POTAMOPYRGUS Stimpson, apparently confined to the 

 extreme northern border of the continent, and perhaps to be re- 

 garded as a straggler from the Antillean and Middle American 

 fauna. LITTORIDINA Eydoux & Souleyet, a characteristic South 

 American genus of slender, acute shells, usually called " Pa/udes- 

 trina," " Hi/drobia " or Heleobia Stimp. LYRODES Doering, possi- 

 bly a group subordinate to Potumopyrgtis. LITHOGLYPHUS 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. Ruthi!. 



The genus Cochliopa Stimpson, with two Central American spe- 

 cies, C. Ron'elli Tryon and C. TryoiiuinaT'ils., is like PotamolUhus in 

 the solidity of the shell, but it is heliciform and umbilicated. Lucn- 

 nopsis and Julllenia, two Cambodian genera, are evidently near akin 

 to the South American Potamollthns (see Journ. de Conchy 1. 1881, 

 p.l). 



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. 



