PBOCEEDINGS OF THE NATIONAL MUSEUM. 341 



in the latter region have inhabited it long- enongh to change specifically 

 from their oriental ancestors. 



J. G. Cooper believes that he found a form of Anodonta nuttaliana^ 

 Lea, one of the Cygnea gnmi), in the Pliocene beds of Kettleman Lake, 

 California,' and in other localities, but these formations may be of more 

 recent date. 



It is probable that Vnio [Marddritana) morf/aritiferns, Linnivus, is the 

 type of a groui) which for a long time has been distributed around the 

 boreal regions, as it seems to be very closely related to a number of 

 widely scattered forms. 



The theory of a comparatively recent land connection between north- 

 ern Asia and North America is further confirmed by the fact that some 

 fifteen species of laud snails, and about five or six more fresh-water 

 forms, are common to the entire boreal regions of the globe ; and Dr. 

 Asa Gray has shown- that there are very many species of plants belong- 

 ing to China and Japan which are identical with those found in eastern 

 Is^orth America, and for others there are exceedingly close representa- 

 tive species in the Xew World. 



The Uuione faunas of the Australian and Neotropical regions may be 

 considered together, as they are evidently closely related. The theory 

 of an antarctic land connection between these regions is not at all a 

 new one, and recently Mr. Charles Hedley, in a paper on "The faunal 

 regions of Australia,'" brings forward some strong arguments in favor 

 of such a connection, as he believes it necessary in order to explain 

 certain relationships between the life of the two regions. The Mutelid 

 fauna of South America is also, no doubt, related more closely to that 

 of Africa than to anything else at present existing, and von Ihering' 

 suggests a probable land connection between South America and Africa 

 across the Atlantic during the Mesozoic, to account for its ]>resent dis- 

 tribution. 



It does not seem to me that it is necessary to bring in any such 

 immense and violent changes of land and sea to account for the presence 

 either of the Mutelida^ in Africa and South America or the nearly related 

 L^nios in the Australian and Neotropical regions. It must be remem- 

 bered that changes take place in the fresh-water mussels very slowly; 

 that si)ecies are living to-day that scarcely differ from those found at 

 the close of the Cretaceous or the beginning of the Tertiary periods; 

 and that the relation between the Mutelidai of Africa and South Amer- 

 ica is not a very close one, so that it is not necessary in either case to 

 prove any recent mingling of these faunas, either by a land way or 

 other means. I believe it is far more probable that the Ilnios of South 

 America and the Australian region are the remnants of earlier types 

 that may have had a wide distribution throughout the northern hemi- 



'Proc. Cal. Acad. 8ci., 2*1 ser., IV, part 1, p. 168. 



-Address before Am. Assu. Adv. Sci., August, 1872, p. 10. 



^Read at the Adelaide meeting of the Australasian Assn. Adv. !Sci,, »September, 18!t3. 



-•Zool. Auzeiger, Nos. 380 and 381, p. 14, 1801. 1892. 



