PILSBRY: NON-MARINE MOLLUSCA OF PATAGONIA. 515 



Chilinidae : Chilina tehuelcha, C. pitelcha, C. parchappii. 

 Lymnaeidae: Lymncea viator, Planorbis peregrinus, P. anatinus. 

 Ancylidae : Ancylns concentricus bonariensis. 

 Amnicolidas : Littoridina parchappii, L. australis. 

 Sphaeriidae : Not reported, but doubtless present. 

 Unionidae : Diplodon patagonicus. 

 Mutelidae : Anodontites puelchana. 



B. Rio Chubitt Fauna. 

 Unknown. 



C. Rio Santa Cruz Fauna}- 



Chilinidae: Chilina strebeli, C. smithi, C. fulgurata, C. f. oligoptyx, C. f. 



livida, C. f. andicola, C. f. hatcheri, C. campy laxis, C. monticola pilula, 



C. lebnmi, C. perrieri. 

 Lymnaeidae : Lymncea viator, L. diaphana, L. d. inelegans, L. patagonica 



riochicoensis, L. andeana. 



Amnicolidae : Littoridina hatcheri, L. simplex, L. sublineata. 

 Sphaeriidae : Musculium patagonictim, Pisidium magellanicum, P. pata- 



gonicum, P. observations. 



D. Magellanic, Fuegian and Falkland Faunas? 



Chilinidse : Chilina patagonica, C. amozna, C.fuegiensis, C. monticola, C. 



fttsca, C. nervosa, C. falklandica. 

 Lymnaeidae : Lymncea diaphana, L. patagonica, L. pictonica, L. brunneo- 



flavida. 

 Sphaeriidae: Pisidium magellanicum. 



These several faunas may be roughly compared with the life-zones of 

 North America. The La Platan zone is equivalent to the Austral, the Rio 

 Negro fauna to the Transition, and the remainder of the Patagonian zone 

 to the Boreal zone of the northern continent. 



The distinctness of the Patagonian faunas A, C, D may be attributed 

 to three main factors: (i) Climate, which imposes limits on the north 

 or south distribution of species. (2) Absence of streams flowing north or 

 south, and the consequent isolation of the river systems, favoring the evo- 



1 Known only from the collections of Mr. J. B. Hatcher. 



2 From the researches of Captain King, Dr. Coppinger, the U. S. Exploring Expedition, the 

 French Expedition to Cape Horn, Dr. Michaelson and others. 



