GEOGRAPHICAL DISTRIBUTION OF NEW YORK UNIONIDJE. 99 



Anodonta edentula, Unio iris, Unio multiradiatus, and Unio 

 rubiginosus are not to be considered as indigenous inhabitants of 

 the Eastern drainage system, as they occur only near the bound- 

 ary of the system and probably are immigrants from the 

 St. Lawrence system. 



Unio fabalis can not be considered a normal inhabitant of the 

 St. Lawrence system. Unio complanatus is doubtfully included 

 in the Mississippi system. 



The most striking feature of the above table is the fact that 

 no species is found in both the Eastern and Mississippi systems 

 unless it is also found in the St. Lawrence system.- Of the fifty- 

 four species considered only eight are confined to a single 

 drainage system, and only five are not found in the St. Lawrence 

 system. The presence of forty-nine of the fifty-four species in 

 some part of the St. Lawrence system, together with the fact 

 that forty- six of these forty- nine are found in one or both of the 

 other two systems, may indicate that the St. Lawrence system 

 was probably the place of origin of some of the species, or the 

 route over which they migrated, or the center from which some 

 species developed into eastern forms and others into western 

 forms. 



