ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 499 
The subgenus Faxonius is represented in our state by three species: CO. limosus, 
OC. propinquus, and C. obscurus. The first is geographically, as well as morpho- 
logically, separated from the other two ; and here again it is the shape of the male 
organs which serves as the chief distinguishing feature. Besides there are other 
characters, such as the shape and the spinosity of the carapace, which make it pos- 
sible to recognize C. limosus at a glance. No transitional forms being present, the 
standing of C. limosus as a “ good species” is beyond doubt. 
It is different with C. propinquus and obscwrus, and the extralimital form C. 
sanbormi. These three resemble each other very closely, and it is hard, indeed 
impossible, without close examination to distinguish them. ‘They also live under 
similar ecological conditions, and their ranges together form a unit, so that it is evi- 
dent that they are closely allied genetically. The differences of C. obscurus from the 
other two forms are furnished by the ‘‘shoulder”’ of the male organ and the tubercles 
of the annulus of the female, together with the complete lack of the median keel of 
the rostrum. Other differences, such as sculpture and spinosity of the chelipeds, 
are of secondary value and not entirely reliable. But it must be emphasized that 
within the established range of C. obscuwrus, from Fish Creek in the southern part of 
the Panhandle of West Virginia to the upper Alleghany and the Genessee Rivers 
in McKean and Potter counties, and from Cheat River at the West Virginia state- 
line, to the upper Shenango River in Crawford County this species is remarkably 
uniform in the characters mentioned. No specimens have been found within this 
area which show the slightest tendency toward C. propinquus. 
Thus, with reference to this form, the postulate that a species should be sharply 
and constantly separated from the coexisting allied forms is fulfilled (see Ortmann, 
1896, p. 191) and accordingly I regard C. obscwrus as a good species. 
As regards C. sanborni, matters seem to be slightly different. It agrees in the 
shape of the sexual organs with C. propinquus, and differs only from the latter in 
the lack of a rostral keel and some minor features in the armature of the chelipeds. 
In the lack of a rostral keel it approaches C. obscwrus, but always may be distin- 
guished by the shape of the sexual organs. Its relation to C. propinquus remains 
doubtful. My observations do not cover the region in which possible transitions 
might be expected (northern and western Ohio), and thus I must leave this question 
open, and I follow Faxon in regarding C. sanborni as a variety of C. propinquus. 
But it should be possible to settle this question by proper investigation, and I would 
not be astonished if it should be finally discovered that C. sanborni actually is a 
good species, sharply and constantly separated from C. propinquus. 
The subgenus Bartonius contains four species in Pennsylvania. One of them, 
