398 CRAYFISHES. 



The closel}^ related Blue oi- Moiiongahela 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. ibibius, and they were recorded as such by Mi'. Williamson in a paper on 

 the Crayfish of Allegheny County, Pennsylvania (Ann. Carnegie Mus., 1901, 

 1, p. 11). Compared with the type of C. duhius 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. dubms, 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 tlie 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 Candxirus 

 inonongalcnsis) 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, l:)etween it and 

 the pi-incijial 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. monongaknsis 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, i. e., C. dubius Fax., and came to the conclusion tliat they 

 represented a distinct species. But as appears from what has been said above, 

 thi'ee 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 



