438 MEMOIRS OF THE CARNEGIE MUSEUM 
dammed up by the ice, and transformed into lakes (Lake Monongahela of White, 
1896, and Lake Ohio, cf. Jillson, 1893, p. 19, and Map, Pl. 5, with the necessary 
restrictions), and this led to the result that the colonies of crawfishes belonging to 
the southern (upper) parts of these rivers became sharply separated from each other, 
and I think that the tendency toward the formation of three species (C. propinquus, C. 
sanborm, C. obscurus) is directly due to this process and to physiographical conditions 
prevailing in the earlier part of the Glacial Period (Kansan or Prekansan, cf. Hice, 
1903, p. 300). 
Finally these lakes were connected and drained off toward the southwest, thus 
forming the present Ohio River (Postkansan, but before the Wisconsin stage, cf. 
Hice, 1903, p. 299); the areas of the three forms of crawfishes were reunited, but 
the different parts of the new Ohio drainage are occupied by different forms of the 
propinquus-group, remaining in their original areas; the upper Ohio is character- 
ized by C. obscwrus, the middle Ohio by C. propinquus sanborni, and the lower Ohio 
by C. propinquwus. 
But additional changes took place in Postglacial times. According to the pres- 
ent distribution these must have been greatest in the case of C. propinquus. 
Almost the entire range of this form lies within the glaciated area, and thus it is 
beyond question that its present distribution is largely due to the Postglacial migra- 
tion northward and northeastward.” This migration possibly began at an earlier 
date than in the case of the other two forms. We know that in southern Indiana 
and southwestern Ohio an early retreat of the southern border of the ice took place, 
as is indicated by the presence of Ilinoisan drift south of the early Wisconsin border 
(cf. Leverett, 1902, Pl. 2 and P]. 11). There also was considerable recession of the 
ice of the Maumee-Miami glacial lobe in the earlier and later Wisconsin stage, while 
in central and eastern Ohio and western Pennsylvania (Scioto glacial lobe and 
Grant River glacial lobe) only in the later Wisconsin stage did recession take place 
(cf. Leverett, ibid., and Pl. 13 and PI. 15). Toward the end of the later Wisconsin 
stage large lakes began to form in front of the receding ice, and this happened first 
in the western part of this region. ‘The first lake thus formed was Lake Maumee 
(Leverett, p. 710 ff., Pl. 20 and 21), which had an outlet toward the west and south- 
west (Fort Wayne outlet; see also Grabau, 1901, p. 58). Lake Maumee was situ- 
ated in northwestern Ohio, in the present Huron-Erie basin, and thus we see that 
the latter was opened first in its western part to an immigration from the southwest 
A loss of territory must have occurred in the south, C. propinquus losing ground in competition with C. rusticus 
which was pushing on from the south. This matter does not belong to our present investigation, but attention should 
be called to it. 
