354 ORTMANN— THE ALLEGHENIAN DIVIDE. [April iS, 



most headwaters, the roughest parts of them, characterized by firm 

 bedrock bottom covered with loose stones and boulders, often shift- 

 ing, chiefly during flood stages. Such conditions are entirely unfa- 

 vorable to crayfishes and N a jades (the latter generally demanding 

 sand and gravel, which is firmly packed), and thus we have here an 

 ecological harrier to the upstream migration of the OJiio fauna, 

 which is absent, for instance, in the upper Allegheny. 



The fact that this fauna is here checked by a modern physio- 

 graphical feature confirms the assumption that the upstream migra- 

 tion of it falls in a rather recent (Glacial and Postglacial) time. 



Excepting these mountain streams just discussed, the uniform 

 Postglacial upper Ohio fauna comprises all the headwaters of the 

 Ohio (Allegheny and Monongahela), and further all the tributaries 

 in West Virginia ; also the fauna of the Big Sandy belongs undoubt- 

 edly here, and we know that this river once was closely connected 

 with the Old Kanawha River (Tight, 1903), and that its history was 

 similar to that of the other rivers, which are ancestral to the upper 

 Ohio system. This is somewhat different in the case of Licking 

 River in Kentucky. Leverett (1902, p. 109) unites this river with 

 the Preglacial lower Ohio (and with the Kentucky, Cumberland and 

 Tennessee rivers). If this is correct, we should expect in this river 

 the Tennessee-Cumberland fauna; but there is no trace of it here,^^ 

 and the Licking fauna is entirely of the same character as that of 

 the rest of the upper Ohio, as far as it concerns the Najades. Of 

 Pleuroceridce a new species turns up here, but this material is too 

 unsatisfactory. But on the other hand a peculiar crayfish is found 

 in the Licking, Camharus rusticus, which distinctly points to the 

 west. But since also Monongahela and Kanawha are characterized 

 by different (although closely allied) species of crayfishes, Licking 

 River also in this particular falls in line with these other streams. 



The physiographical evidence with regard to the history of Lick- 



" See p. 309. The fauna is not completely known, but according to my 

 collections, only one species turns up, which is absent in other parts of the 

 upper Ohio drainage discussed here: Anodontoides ferussacianiis. All the 

 rest is typically upper Ohioan. It also should be noted, that one species, 

 Lampsilis luteoJa, is present here, which is absent in the Cumberland-Tennes- 

 see fauna. 



