OKTMANN : THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 401 



ADDITIONAL LOCALITY. 

 The writer has seen this species at Sandy Creek, Allegheny County, Pa. 



REMARKS. 



The Blue Crawfish is rather abundant in the region indicated by the above 

 localities, and apparently represents a geographical differentiation of C. carolinus, 

 the Red Crawfish. The points in which it differs from the latter species, aside from 

 color, are slight, but are constant according to my observations. 



The rostrum is markedly different from that of C. carolimis, although slightly 

 variable. It always is smaller than that of the latter species and narrower, with less 

 distinctly marked lateral angles. The lateral margins are swollen, but the swelling 

 is less marked, and does not suddenly decrease at the lateral angles. The degree of 

 convergence of the margins is variable, but generally much more pronounced than 

 in the Red Crawfish; cases like that figured in Plate XXXIX, Fig. 4b, are rather 

 rare, in fact, this case forms the extreme in this direction. 



In the shape of the hand, the rounded outer margin and the absence of .serra- 

 tions on it are other striking characters of this species ; and the carpopodite is dis- 

 tinguished by the larger number of spiniform tubercles, as described above. The 

 outer lower margin of the meropodite generally has a blunt and smooth keel, with 

 only one small tubercle near the distal end (which may be absent). Among my 

 material I had only ten specimens which revealed an exception, where two such 

 tubercles were present, and in onl}^ two of them were these tubercles present on both 

 chelipeds. In the others they occurred only on one side. There ai-e instances in 

 which a large number are found, but always in claws which have been regenerated. 



Aside from tlie slight variations indicated above only a few exceptional cases 

 have been encountered in which niarkLMl deviation from the above description 

 of the prevalent colors occurs. The blue ground-color is always present on the 

 anterior part of the carapace and the chehv. In a rare variation, which has 

 l)een observed about half a dozen times, the grounil-color of the posterior part of the 

 carapace and parts of the abdomen are more or less purplish {attricitla-jinrplf, \'I1I, 

 3). Furthermore a single adult female was found at Monaca in whiih all red tints 

 were absent ; the blue of the bod}' was very clear, the margins of the rostrum were 

 blue like the carapace, the finger tips were whitish, all spines and tubercles were 

 pure white, and the antennal flagelluni was a pure blue. Specimens in which the 

 margins of the rostrum have the same shade of IjUie as the carapace are not 

 infrequent. 



