450 MEMOIRS OF THE CARNEGIE MUSEUM 



it has crossed the continental divide, and has invaded the Allegiiany River drainage 

 in McKean, Warren, and Crawford Counties, and possibly has come down the 

 Alleghany River as far as Allegheny Count3% spreading into some of its smaller 

 tributaries."" This assumption seems plausiV)le if we take into consideration only the 

 Pennsylvanian material and that tVom the St. Lawrence Basin. Wo would have 

 here a case of distril)Ution which is entirely unique. C. Jxirtorii rohiistus should 

 then be regarded as a Postglacial form, which originated in the St. Lawrence 

 drainage, and in Pennsylvania spread southward, coming fi'om the north. 



But there are objections to this view. C. hartoni rohushts has been reported also 

 from Virginia, Maryland, and Kentucky, and this, of course, would not be in favor 

 of this theory. However, as has been said above (p. 392), I am inclined to believe 

 that this southern form is not the same as the northern. If this view should be 

 correct, I should regard C. robasfns as a good species, and then the above opinion 

 would hold good. 



But further, the morphological characters of C. hdiinni roJxiMux, as compared 

 with those of the typical hartoiii, are distinctly more primitive. The shape of the 

 rostrum is decidedly more archaic, the original form of the rostrum in the subgenus 

 Barformis being rather elongate, and not short and broad as in ('. Ixirioni. The 

 frequent presence of distinct lateral spines on tlie carapace is undoulitedly a primi- 

 tive character; and the ecological peculiarity of prefei-ring larger streams than are 

 haunted by the typical fjrm might also be I'egarded as a remnant of more piimitive 

 conditions. This, of course, would be strange in a Postglacial form, originating within 

 the glaciated area, and we rather ought to expect a higher differentiation than the 

 original, typical form. 



Until the question of the identity of our northern C Innioni mJiuMuf! with the 

 southern form, which bears the same name, is settled, we cannot form a tiiial opinion. 

 If both forms should be actually identical, we might have to deal with two races of 

 (J. hartoni, an older one (C. bartuni rohvdus), Avhich possibly constituted a first wave 

 of migration from southwest to northeast, which was overrun and crowded out by 

 a later wave, consisting of C. Ixuioiti fijpicus. Remnants of the older stock have 

 been alile to survive only at a few, scattered localities in the south, while in the 



'"The Alleghany Kiver, between Sandy Creek and Verona, lias been investigated repeatedly. It is a curious fact 

 that Dr. D. A. AtkiDson collected here a large number of C nl>«ciiriis on September 17, 1900, but not a siugle rubnstns. 

 I was at the same place on June 1, 1004, together with Dr. Atkinson and Dr. O. T. Cruikshauk, but we did not collect 

 this form (conditions were unfavorable) ; on November 19, 1904, I spent a whole day there, collecting numerous C. nb- 

 scurus, and a few C. hartoin (typical ), but not a single ro6Hs(»swas seen. When I visited thisplace again, on September 

 7, 1905, I secured within a short time six specimens of C. hartoni robustus, and on September 30, 190.5, I found three fine 

 specimens a little further up the river, at Hulton, although I did not hunt very diligently. Is it possible that the 

 migration of this form down the river is going on ? Does it gradually become more abundant ? 



