ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 429 
form actually came by the way indicated some traces of its former existence should 
have been left in Pennsylvania, Maryland, or the Virginias, chiefly since there was 
no competition by any other species, river-forms being absent in the Alleghany 
Mountain region. Thus the direct route across the mountains seems to be out of 
the question, and this is further rendered probable by another consideration. 
C. limosus being ancient, its migration eastward must have taken place at a re- 
mote epoch, certainly at an earlier time than that of a group which is more advanced, 
namely, the propinquus-group. As we shall see below, the latter existed already in 
Preglacial times, and thus we are forced to place the origin of the limosus-group at 
least as far back as the Tertiary. During this time, however, the Ohio in its present 
form did not exist. There was Spencer River,* in West Virginia and western Penn- 
sylvania, and another river (Old Kanawha) * in West Virginia and Ohio, running 
northward to the Erigan River, which 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. Lawrence basin, 
possibly also to the Erigan River (White, 1896, p. 376). All these rivers flowing 
northward in Pennsylvania and Ohio were different in character from what the 
rivers of this region are now. ‘Their fall was slight, and they were rather sluggish. 
This is positively known of the Spencer River (or the Old Monongahela), which 
must have been practically at base-levei (White, 1896, p. 377). If this was the case, 
nothing is opposed to the assumption that C. limosus (or its ancestral form) once was 
an inhabitant of some of these rivers. But 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 limosus-group to 
the north, 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- 
‘SSee Foshay, 1890, p. 368 ; Leverett, 1902, p. 89. 
*See White, 1896, p. 376 ; Leverett, 1902, p. 100; Tight, 1903, map, Plate I, Plates 16and17. (Teays River.) 
‘5 See Spencer, 1881, map 2, and 1894, p. 293. 
