372 ORTMANN— THE ALLEGHENIAN DIVIDE. [April 18, 



donta marginata, but reversed, and that the original range was on the 

 east side, and that the upper Kanawha received it from the east, 

 probably by stream capture, since transport over land is not very 

 likely on account of the improbability that birds (or other crea- 

 tures) carried this species only into the Kanawha, and refused to 

 do so into other western streams. 26 



But as we have seen above, it is not probable that the upper 

 Kanawha has captured any streams of the eastern drainage, but 

 rather the reverse is true (above, p. 346 f.). The present course of 

 New River represents most nearly the ancient drainage features, 

 while the eastern streams (Roanoke, James and possibly also Po- 

 tomac) have captured sections of the old New River and Greenbrier 

 system. New River runs within the mountains on a distinctly 

 higher level than most of the other streams which have cut much 

 more deeply into the Cretaceous base-level, and thus had a better 

 chance to capture parts of New River, than vice versa (see PI. XIV., 

 fig. 1). 



This induces us to assume that Symphynota tappaniana origi- 

 nally was a local form of the New River drainage, developed prob- 

 ably out of the western 5\ compressa as an ecological mountain- 

 form. In this case it is strange that the range of S. compressa does 

 not come very near to that of 5\ tappaniana, but this may be due to 

 a subsequent restriction of the range of S. compressa. 27 



26 There is, however, one fact in favor of this assumption. S. tappaniana 

 is one of the few cases of hermaphroditism known in Najades. If we grant, 

 that in rare cases, specimens have been transported, we must admit the pos- 

 sibility that a new stream might have become stocked with this species, by the 

 transplantation of a single individual. But then again, we do not know, 

 whether self-fertilization occurs here. I mention this here, to bring out all 

 possible arguments. 



27 The nearest place known to me for S. compressa, is Little Kanawha 

 River, where it is very rare, and also this locality is isolated. Forms like 

 S. compressa and tappaniana seem to be absent in the upper Tennessee 

 drainage, but in the latter is Symphynota holstonia (which is not an Alasmi- 

 donta), and a very doubtful, incompletely known species, S. quadrata (Lea), 

 which has a certain external resemblance to 5. tappaniana, but may be any- 

 thing. vS. holstonia is surely not closely related to 5\ tappaniana, for it has no 

 lateral hinge-teeth. It remains to be seen, whether there are any related 

 forms in the upper Tennessee, which, when present, might suggest, that New 

 River received its species from the Tennessee. 



