PILSBRY: NON-MARINE MOLLUSCA OF PATAGONIA. 631 



3. The Naiades or fresh-water mussels found in all of the continents, are 

 represented in Australia, Tasmania and New Zealand only by species 

 which have been referred to the genus Diplodon. This genus is widely 

 distributed in South America, especially southward. It is a relatively 

 primitive genus and probably arose in South America, which, from the 

 number of autochthonous genera, was evidently an old evolution center 

 of Naiades. Diplodon is unknown in the northern continents. Whether 

 the relationship with South American forms claimed for the Australia- 

 New Zealand group is well-founded, remains to be confirmed by careful 

 comparison of the soft anatomy. 



The family Endodontidce, and Gtindlachia of the Ancylidce, have been 

 considered "Antarctic" groups, but on evidence of slight value. The 

 Endodontidce are an ancient group, world-wide in distribution. No close 

 relationship has been shown to exist between the South American and 

 the Australian genera. The former are unknown anatomically, and the 

 relations of Australian and New Zealand forms, so far as positively made 

 out, are with the groups of Polynesia and Micronesia ( Charofia, Thauma- 

 todon, etc.). Certain Tasmanian species may prove to belong to the 

 American genus Radiodiscus Pils. See p. 516. 



Gundlachia is found in Australasia, South America, the Antilles, Mexico, 

 temperate North America and also the Miocene of central Europe. This 

 wide distribution suggests that the genus may have reached the southern 

 lands from the north. In the United States it has been found in Cali- 

 fornia, Illinois, Ohio, New York, etc., but only at remote intervals and in 

 very narrowly restricted areas. It is likely that it will turn up sooner or 

 later in the Oriental region and Africa. I hesitate to claim Gundlachia 

 as an inhabitant ,of Antarctica. 



Pond snails of the family Lymnceidce also occur in all the Austral 

 lands, but South American forms do not seem especially related to Austral- 

 asian. While Endodontidce, Gundlachia and Lymncea may have inhabited 

 Antarctica, no data upon them now in our possession goes far towards 

 proving that they did. 



I can find no evidence to support Hedley's contention that the Macro- 

 ogona (Accmidce] of Tasmania and Australia, and the Rhytidida of the 

 same regions, New Zealand, New Caledonia, etc., are " of Antarctic origin." 

 These groups must have attained their distribution from South Africa to 



1 Hedley, Proc. Linn. Soc. N. S. Wales, 1899, pp. 396, 398. 



