ORTMANN: 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. carolinus, 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 XX XIX, 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 only two of them were these tubercles present on both 
chelipeds. In the others they occurred only on one side. There are instances in 
which a large number are found, but always in claws which have been regenerated. 
Aside from the slight variations indicated above only a few exceptional cases 
have been encountered in which marked 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 chele. In a rare variation, which has 
been observed about half a dozen times, the ground-color of the posterior part of the 
carapace and parts of the abdomen are more or less purplish (awricula-purple, VIII, 
3). Furthermore a single adult female was found at Monaca in which all red tints 
were absent; the blue of the body 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 flagellum was a pure blue. Specimens in which the 
margins of the rostrum have the same shade of blue as the carapace are not 
infrequent. 
