NO. i20o. .s r \OPSIS OF THI: y.irADKssTMPsos: 505 



number of forms are found in each of them that are not at all closely 

 related to any of those of the other. 

 These regions may be tabulated as follows : 



ARKAS OF THE NAIAD REGIONS. 1 



Europe. 



Northern ami Western Asia. 



Palearctic 



North Africa to the Desert. 

 I'ucitic drainage of North America. 



Ethiopian Africa, south of the Sahara. 



Orient-il (Asia, south of the Himalayas. 



lEast Indies to the Solomon Islands. 

 [Australia. 



Australian -Tasmania. 



<-New Zealand. Part of New Guinea. 



Neotropical South America. 



[Central America. 



Central American-. Mexico, east of the Cordillera. 

 LCuba. 



Entire Mississippi Valley and the Golf drainage from west Florida 

 to the Rio Grande. 



Mississippiaii Mackenzie River system. 



Red River of the North. 

 Great Lakes. 



Atlantic " I Lower St. Lawrence and rivers of eastern Canada. 



I Atlantic drainage of the United States. 



I have hesitated long before placing a considerable number of the 

 species of Southeastern Asia in and near North American genera. I had 

 hoped to be able to examine the soft parts of a number of these Oriental 

 forms, but have been disappointed, and as nothing is known of the 

 anatomy of most of them I have been compelled to classify by shell 

 characters alone. It is certain that the beak sculpture of a large num- 

 ber of Naiades of this area is essentially concentric, and not zigzag 

 radial, as it is in most of the forms of the Oriental region. The shell 

 characters of the ponderous Chinese Uniones are certainly much like 

 those of Quadmln, in the form, the teeth, the beak sculpture, and 

 especially the deep, compressed beak cavities. A great number of fossil 

 forms from the Tertiary strata of Asia and Eastern Europe seem to 

 show the closest relationship to the American Quadrulas. Hyr tops-is, 

 Cristaria, Chamberlainia, and Pilsbryoconcha seem to be related by 

 shell characters to the alate forms of Lamps-ills, and even the strange 

 Pseudospatha of Africa would appear to belong here. 



I recognize about one thousand species and 82 varieties of Uuionidre, 

 having reduced to the synonymy a great many names that most authors 

 have believed to stand for valid species. Of these, 533 species and 55 

 varieties belong in North America and 101 in South America. The 

 list contains 117 species of Mntelidne and 11 varieties, and of these 80 



1 For map of Naiad Regions see plate. 



