MEMOIRS OF THE CARNEGIE MUSEUM 
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REMARKS. 
Cambarus obscurus is the river species of the Upper Ohio drainage. It is widely 
distributed in western Pennsylvania. Compared with the allied species C. propin- 
quus, Which occupies a much wider area, it is rather uniform in its characters all 
over its known range. It nowhere reveals a tendency to vary in the direction of 
C. propinquus, or of propinquus sanborni. This is the more remarkable because C. 
propinquus distinctly inclines toward this species in Erie and Crawford Counties, (in 
the lake drainage), and likewise because C. propinquus sanborni shows such a ten- 
dency in Wetzel County, West Virginia. 
The variations observed in our abundant material have been briefly indicated 
above. However, it deserves special mention that the specific characters are 
searcely subject to any variation. 
Very interesting conditions are offered by the spines of the outer lower margin 
of the meropodite of the cheliped. One or two spines may be present, the prox- 
imal one smaller and often represented only by a small tubercle. Looking over our. 
material, I find that only one spine is present in all individuals from the upper 
Alleghany drainage, including all the tributaries from Red Bank Creek northward 
(sixty-one specimens are at hand). In Armstrong, Indiana, Westmoreland, and 
Allegheny Counties, in the drainage of the Alleghany River, and in the whole 
drainage of the Monongahela, the Beaver, and Ohio proper, a second spine may be 
present, but such cases are not frequent, and generally this spine is found only on 
one of the two chelipeds. ‘There is a tendency of this character, more frequently 
displayed in the southwestern extremity of the range. ‘Two such spines on either 
side (right and left) are very rare, and I have found them only in twenty speci- 
mens; fifteen of which belong to the Ohio drainage: two to that of the Monongahela, 
six to that of the Beaver, and seven to that of the Ohio below Beaver. ‘Two cases 
were discovered in Wills Creek, Maryland, and three in Conneaut Creek at Albion, 
Erie County, Pa. 
The latter specimens are interesting inasmuch as in Erie and Crawford Counties 
two drainage areas come together with that of Lake Erie, namely, that of the 
Shenango River, a tributary of the Beaver, and that of French Creek, a tributary 
of the Alleghany. In the latter creek and its tributaries I have never seen 
an individual with two spines (seventeen specimens are at hand). Among the 
material from the Beaver River drainage (fifty-six specimens) there are twenty- 
one with two spines. Thus the tendency to develop two spines is markedly present 
in the drainage of the Beaver, while it is apparently absent in French Creek. 
