548 PATAGONIAN EXPEDITIONS: ZOOLOGY. 



Family AMNICOLIDCE Tryon. 



Amnicolidce Tryon, Proc. Acad. Nat. Sciences of Philadelphia, 1862, p. 



147 ; Gill, Proc. A. N. S. Phila., 1863, pp. 33, 35. 

 Hydrobiince Stimpson, Researches upon the Hydrobiinae and Allied 



Genera, 1865, p. 4. 

 Hydrobiidce Fischer, Manuel de Conchyliologie, 1885, p. 723. 



This family of minute river-snails has been but little studied or col- 

 lected in South America. We have some knowledge of the species of 

 the Rio de La Plata system though the work of d'Orbigny, Doering and 

 Strobel and collections made by Dr. W. H. Rush, U.S.N. In south- 

 ern Brazil Dr. von Ihering has done good work, though hampered by 

 the want of La Platan material for comparison. In Ecuador K. Miller 

 has described a few forms collected by Wolf and others. In the north, 

 Dr. von Martens has recorded a few Venezuelan species. None are 

 known from the Orinoco or Amazon systems. Through the collections of 

 Mr. Hatcher we are now enabled to add several forms from Patagonia. 

 The opportunity has also been taken fully to describe and figure the 

 known species of Potamolithus, part of them new forms, most of the rest 

 hitherto defined only by a brief "key" published in 1892. Only six of 

 the thirty species now known have hitherto been figured. 



All of the South American genera and species of Amnicolidce are de- 

 scribed or referred to below. 



The following genera of this family are represented in South America : 



Amnicola Gould and Haldeman, Idiopyrgus Pilsbry, 

 Littoridina Souleyet, Potamolitkus Pilsbry, 



Potamopyrgus Stimpson, Lithococcus Pilsbry. 



Of these genera, Amnicola has been found only in the extreme north. 

 A. ernesti (Martens) of Lake Valencia, Venezuela, is closely related to 

 A. panamensis Tryon and several Mexican species, and is undoubtedly 

 of North American origin. * 



Potamopyrgus is the dominant genus of Amnicolidce in New Zealand 

 and Tasmania. It is unknown in the Oriental region. In America it 

 extends from Argentina to Venezuela, through Mexico to central Texas 

 and throughout the West Indies. This distribution is explicable on the 



* Hydrobia (Amnicola) ernesti Martens, Die Binnenmollusken Venezuelas, 1873, p. 209, Taf. 2, 

 fig. 12. 



