ORTMANN : THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 429 



ionn :u-Uiully came l)y the way indicated some traces of its former existence should 

 have been left in Pennsylvania. Maryland, or the \'irginias, chiefly since there was 

 no competition l>y any other species, river-forms being absent in the AUeghaiw 

 Mountain region. Thus the direct route across the mountains seems to be out of 

 the question, and this is further rendered probable liy another consideration. 



C limosus being ancient, its migration eastward must have taken place at a re- 

 mote epoch, certainl}' at an earlier time than that of a group which is more advanced, 

 namely, the jJi'opinqniin-grouii. As we shall see beloAV, the latter existed already in 

 Preglacial times, and thus we are forced to place the origin of the limo.<ias-gnm\) at 

 least as far back as the Teiliary. During this time, however, ilie Ohio in ite pr(i<riit 

 form did not crixl. There was Spencer River,^'' in ^^'est Virginia and western Penn- 

 sylvania, and another river (Old Kanawha)^ in West Virginia and < >hio. running 

 northwaid to the Erigan Piver, wliich transversed the basin of Lake Erie.*'' And 

 further the present upper Susquehanna (North Branch) is apparently new. It must 

 have taken in Preglacial times a northward route toward the St. Lawi-ence l)asin, 

 possibh' also to the Erigan River (White, 1896, p. 376). All these rivers flowing 

 northward in Penns3'lvania and Ohio were different in character from what the 

 rivers of this region arc now. Their fall was slight, and they were rather sluggi.sh. 

 This is {)()sitively known of the Spencer River (or the Old ^h)nongahela), which 

 must liave been practically at base-level (White, 1896, p^. 377). If tliis was the case, 

 nothing is opposed to the assumption that C. Hmosuti (or its ancestral form) once was 

 an inhabitant of some of these rivers. Put then we see that its eastward migration 

 cannot have been in a direct route, but must have gone on in a roundabout way, 

 chiefly by the old Erigan River. 



If the Erigan River was tributary to the ^Mississippi system, this is easy to 

 imagine. If it drained to the St. Lawrence Gulf, as Spencer believes, we must 

 assume an earlier crossing of the continental divide by this form, wherever this was 

 situated (Indiana?), and then again a crossing of the divide between the Erigan 

 River and the Atlantic coast drainage. 



Be this as it may, we are forced to move the old range of the /i?«o.s-Hs-group to 

 the noith. into the Erigan River drainage, and this gives us the means of explain- 

 ing the discontinuous range of this group. If it were at one time present in an area 

 extending from Kentucky and Indiana through Michigan into Ontario, and if we 

 assume that it crossed over into the Atlantic drainage somewhere in northern Penn- 



'» See Fosliny, 1890, p. 368 ; Leverett, 1902, p. 89. 



«'Sce Wliite, 1896, p. .■{76 ; Leverett, 1902, p. 100 ; Tiglit, 190:i, ninp. Tlntc I, I'latra 16 iiiiil 17. (Tenys River.) 



" Sec Spencer, 1881, map 2, aud 1891, p. 293. 



