I9I3-] ORTMANN— THE ALLEGHENIAN DIVIDE. 375 



opposite direction. Nevertheless, there might have been cases where 

 in the headwater region smaller streams have been deflected from 

 the Holston or Clinch to the Xew River, and since Anculosa is an 

 abundant small-creek-type, it might thus have managed to get across. 

 But in this case also transportation is to be considered as a possible 

 means, since many of the headwaters originate in the same longi- 

 tudinal valleys, and come very close to each other without sharp 

 barriers between them. But the fact that the species in the two 

 systems are sharply distinct speaks against this, for if transport 

 had been possible once, it should have been possible repeatedly, 

 .which would have prevented specific isolation. 



Cambarus longulus. 



The distribution of this species again agrees, in a general way, 

 with that of Sympliynota tappauiaua and of Anculosa, but is rather 

 more restricted on either side. 



It is extremely common in the whole Greenbrier and Xew River 

 drainages. It is also found in the upper Tennessee. On the eastern 

 side it is common in the James drainage, but has not been found in 

 the Roanoke, and besides, it has been reported from the uppermost 

 Shenandoah (Waynesboro, Augusta Co., Ya.) . Farther north, chiefly 

 in the rest of the Potomac drainage, it is positively absent, and also 

 on the west side it does not go into the upper Monongahela system 

 (as Anculosa does). 



Its presence in Xew River and Tennessee in forms which are spe- 

 cifically identical shows a closer connection of these two faunas 

 than in any of the previous cases. We have seen that in Cambarus 

 bartoni, a closely allied species, general distribution is very likely 

 due to active or passive migration across divides. This might be 

 true also here. But Cambarus longulus differs from C. bartoni in 

 its ecological habits, inhabiting preferably larger mountain streams, 

 and not the smallest headwaters or even springs, as C. bartoni does. 

 For all practical purposes we may compare C. longulus with Ancu- 

 losa, and whatever the means were which permitted Anculosa to get 

 from the Tennessee into the New River, might have worked as well 

 in the case of this crayfish. Having reached the New and Green- 



