398 CRAYFISHES. 
The closely related Blue or Monongahela Crayfish was first discovered at 
Pittsburgh, Pa., in 1898, by Mr. E. B. Williamson. Specimens were sent to 
me in the month of August of that year, which appeared to me to be a local form 
of C. dubius, and they were recorded as such by Mr. Williamson in a paper on 
the Crayfish of Allegheny County, Pennsylvania (Ann. Carnegie Mus., 1901, 
1, p. 11). Compared with the type of C. dubius these specimens showed a 
narrower rostrum with less pronounced angles at the base of the acumen; the 
outer border of the hand was evenly rounded, not ridged, and destitute of the 
imperfect serrature seen in C. dubius, where this feature results from the regular 
row of transversely elongated marginal punctations giving to the margin a 
milled appearance; further, the carpus of the Pittsburgh form was armed with 
several accessory spines and tubercles, besides the prominent internal median 
spine which is all the armature of the carpus in C. dubius. 
In a paper on the Crawfishes of western Pennsylvania published in 1905 
(Ann. Carnegie Mus., 3, No. 2) and in a more elaborate memoir which appeared 
at the close of the following year (The Crawfishes of the State of Pennsylvania, 
Mem. Carnegie Mus., 2, No. 10), Dr. A. E. Ortmann showed that the Blue Cray- 
fish and C. dubius both lived in western Pennsylvania, that they occupied differ- 
ent areas separated by the Chestnut Ridge, a range of hills on the west of the 
Allegheny Mountains, the Blue Crayfish (to which he gave the name Cambarus 
monongalensis) being found on the hills lying on the west of this range while C. 
dubius lived in the mountain region to the east of Chestnut Ridge, between it and 
the principal range of the Allegheny Mountains. Dr. Ortmann also brought 
out clearly, as a result of extensive field study, the color-difference between the 
two forms, the dominant color of C. dubius being red, of C. monongalensis blue. 
The range of the latter form appears to be rather narrow, being restricted, as far 
as is shown by Dr. Ortmann’s most interesting investigations, to Westmore- 
land, Allegheny, Beaver, Washington, Fayette and Green Counties, Pa., and 
Hancock, Brooke, Ohio, Marshall and Monongalia Counties, W. Va., at altitudes 
ranging from 800 feet to 1200 feet above the sea-level. 
Dr. Ortmann compared his specimens of C. monongalensis with the northern 
race of C. carolinus, v1. e., C. dubius Fax., and came to the conclusion that they 
represented a distinct species. But as appears from what has been said above, 
three of the characters which Ortmann thought were peculiar to C. monongalensis 
are also present in the southern, typical form of C. carolinus, viz., the narrower 
rostrum, non-serrated outer margin of the hand, and the presence of more than 
one spine on the inner side of the carpus. There are thus left but two features 
