1 2O ADAMS. 



relative in Japan, and also Boycria, with three species, one 

 species each in Japan, United States and Europe. Our luna 

 moth (Tropcea lima) has a close relative in China (sclcne Leach). 

 The Bryozoan genus Pectinatella, although mainly of Northern 

 distribution in the United States, has two species, one in Eastern 

 United States, and the other (P. gdatinosa) in Japan. 



This oriental relationship has been clearly pointed out with 

 regard to some of our Unionidae by Simpson ('96, p. 330). He 

 says : " The Naiad fauna of this region [Oriental] is magnificent 

 and diversified, and almost rivals that of the Mississippi Valley 

 in vigor, size, solidity and variety of forms. Both Dr. C. A. 

 White and von Ihering believe that the Unios and Anodontas of 

 this area are closely related to those of the central part of North 

 America. Not only does there seem to be a general relationship 

 among a large number of the Naiads of this province with those 

 of the Mississippi basin, but several oriental groups are apparently 

 so close to those of our own region that it is well-nigh impossible 

 to separate them. Thus, the Asiatic Anodontas, typified by A. 

 woodiana Lea if found in the United States, would be placed by 

 most students with A. plana ; the Chinese Unios of the group of 

 U. Jiousci Lea, and myersianus Lea, are evidently quite near the 

 Alatns assemblage ; Unio sitpcrbns Lea, is veiy much like our 

 U. capax Green, and a number of the tuberculate forms of China 

 could almost be placed in the American groups of U. lacJiry- 

 mosits and U. pustulosus." As has been said before, it is well 

 known that the Unionidae fauna of the Mississippi River system 

 has been derived from that of Southeastern United States. It is 

 important to notice that the East Asiatic affinities are so distinctly 

 marked in the case of thefrcs/i water fauna. 



The same explanation which Asa Gray gave for the flora, 

 doubtless holds for the fauna. In Preglacial times the flora had 

 an extensive boreal distribution, as shown by Greenland fossils ; 

 and with the advance of the ice, life was driven South in both 

 hemispheres, and has been preserved in both, in favorable locali- 

 ties. An analogous case in the other hemisphere is the preser- 

 vation of certain mammals in Africa and in the Oriental region 

 (Osborn, 'oo, p. 57) and Unionidae (Simpson, '96, p. 340). 



