I9I3-] ORTMANN— THE ALLEGHENIAN DIVIDE. 367 



4. AnculosQ dilatata and carinata. 



5. Cambarus longulus. 



The peculiarities of distribution in each of these cases have been 

 shortly characterized above (p. 357) for the western side of the 

 mountains, and it will be remembered that none of them are fully 

 alike in all particulars, although resembling each other to a degree. 

 This is also so on the eastern side. Thus it is best to take them 

 up one by one. 



Strophitus edentidns. 



This species has a rather general distribution, but it is peculiar in 

 so far as it is one of the two species of Najades which alone are 

 found in the mountain-tributaries of the Monongahela (Youghio- 

 gheny and Tygart), while it is missing in the upper Kanawha 

 region. 19 This forbids it to place this species simply with those 

 which (like the Sphcuriidcu and Campeloma decisum) have a uni- 

 versal distribution east and west of the divide. Indeed, the gen- 

 eral distribution of Strophitus, for instance in Pennsylvania, might 

 suggest that this form has exceptional means of dispersal, and 

 might be transported from one drainage into another. 20 But its 

 absence in the New River system speaks against this, for we cannot 

 imagine that any means (birds for instance), which would have 

 been able to carry this species across divides, should have carefully 

 avoided the New River system. 



Strophitus edentulus is a form eminently characteristic for small 

 streams, and is rare or missing in large rivers. In the upper Alle- 



19 This negative statement might be doubted. But at the four localities, 

 where I collected Najades (Ronceverte in Greenbrier River; Hinton and 

 Pearisburg in New River; Wytheville in Reed Creek), shells were abundant, 

 and in every case / hunted for this species, examining carefully also dead 

 shells lying around; but no trace of Strophitus was discovered. 



20 In order to bring out all facts, which possibly might have a bearing 

 upon this question, it should be mentioned, that Lefevre and Curtis (Science, 

 33, 191 1, p. 863, and Bull. Bur. Fish., 30 (for 1910). 1912, p. 171) have recently 

 discovered a remarkable circumstance in the life-history of this species, dif- 

 ferent from all other known Najades: the larvae (glochidia) of Strophitus 

 undergo their metamorphosis without a parasitic stage on fishes. For the 

 present, however, I could not tell how this could favor passive transport of 

 the young shell. But the fact should be kept in mind. 



PROC, AMER. PHIL. SOC, LIT. 2IO F, PFTNTED JULY II, I913. 



