I9I3-] ORTMAXX— THE ALLEGHEXIAX DIVIDE. 379 



River estuary northward, and goes probably a little farther south 

 on the Coastal Plain into Virginia. In this distribution it would 

 agree very well with the northern stock of the Atlantic fauna. But 

 it differs from the members belonging to this in that it has no repre- 

 sentative species in the upper Ohio basin. However, it is found on 

 the western side of the Alleghenies and is widely distributed in the 

 lake drainage, chiefly in Lake Erie and the state of Michigan, and 

 it is absolutely the same form that is found there. The fact is that 

 these ranges are not disconnected, but appear to be rather continuous 

 across the state of New York and the known localities follow in 

 a general way the line of the present Erie canal from Buffalo to the 

 Hudson River at Albany. This region lies outside the scope of the 

 present paper, but it should be mentioned here that there are other 

 western species of Najades which follow the same line of dispersal 

 eastward from the St. Lawrence drainage to Hudson River. It is 

 very likely that Eurynia nasuta belongs to this group, and it prob- 

 ably is the one of them which has reached in modern times the 

 widest dispersal upon the Atlantic side. Its western origin is con- 

 firmed by the fact that the only species allied to it, Eurynia sub- 

 rostrata (Say), is western and is found in the central and western 

 parts of the interior basin in large, quiet rivers, ponds and lakes, 

 avoiding rough water and strong current. For this reason, prob- 

 ably, it is not found in the upper Ohio drainage. This species has 

 crossed somewhere in the region from northern Illinois to northern 

 Ohio into the lake drainage, developed there into the species nasuta, 

 which then spread eastward, following the quiet waters of the lakes 

 and those of the canal till it reached the estuary of the Hudson. 

 Thence it had no difficulty to spread farther over the Coastal Plain 

 and reached across New Jersey 30 the lower Delaware, and even be- 

 yond. Also on the Atlantic side it preserves its preference for lakes, 

 estuaries, canals, etc., that is to say, for quiet water. 



We thus are to regard Eurynia nasuta as a quite recent immi- 

 grant in the Atlantic drainage, belonging surely to the Postglacial 

 time, and this immigration might have been completed even by the 



30 It is present, for instance, in the Delaware-Raritan canal at Princeton, 



N.J. 



