Il8 ADAMS. 



shell fauna. Mr. Charles T. Simpson, of the U. S. National 

 Museum, has told me that within 200 or 300 miles of Chatta- 

 nooga there are more valid species of Unionidae than in all the 

 rest of the world. As to the Pleuroceridae, about 300 or 400 

 species are found in this same area. These and the Viviparidae 

 here reach their largest size. Here also is the maximum differ- 

 entiation of the crayfish. The states of Georgia, Alabama and 

 Tennessee, have, according to Faxon ('85, p. 179), the richest 

 crayfish fauna 36 species. 



The vertebrate fauna is also very rich. Jordan ('96, p. 114) 

 says of the fish fauna : " These conditions [favorable for fish] are 

 all well realized in the Washita River of Arkansas, in the various 

 tributaries of the Tennessee, Cumberland, and Ohio, and in these 

 streams, among the American streams, the greatest number of 

 species have been recorded." 



ENDEMISM AND RELICTS IN THE FAUNA. 



There is still another line of evidence which indicates that this 

 region is not only a recent center of dispersal, but in addition, an 

 area of preservation of ancient types. While it is in this region 

 that the indigenous fauna of Eastern United States reaches its 

 greatest development, it is not these forms primarily to which I 

 wish to call attention now, but to the relicts or fragments of a 

 still more ancient fauna. For convenience these will be discussed 

 in two groups : 



i. Relicts Jiavihg Asiatic Affinities. Years ago Asa Gray ('78), 

 and Hooker ('79), and more recently Sargent ('94'), have dis- 

 cussed the close relationship existing between many plants found 

 in Eastern America; and others found in Japan or Eastern Asia. 

 This discontinuous distribution of many of these forms indicates 

 that they are fragments of an ancient flora. Hooker says : " This 

 generic identity, however, gives but a faint idea of the close rela- 

 tionship between East American and East Asiatic, especially of 

 the Japanese floras, for there is further specific identity in about 

 230 cases, and very close representation in upwards of 350; and 

 what is most curious is that there are not a few very singular 

 genera of which only two species are known, one from east Asia, 

 the other in east America." The tulip tree (Liriodendroti), bald 



