ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 5OL 
no doubt that C. diogenes is a good species, and even when discovered in company 
with C. monongalensis or C. carolinus we found no intermediate forms which might 
render the identification uncertain. 
As has been demonstrated above, there are two races of C. diogenes in Pennsyl- 
vania, an eastern and a western. They never have been distinguished before, and 
indeed are very similar, so that it is hard to tell them apart. But I think Iam 
able to do so. The differences are very slight, but I never observed intermediate 
forms, and their existence is improbable, the ranges of the two races being widely 
distant from each other. The constancy of the differential characters being the 
only criterion of specific difference, while the amount of difference is of no con- 
sequence at all,* we might regard the eastern form as a different species from 
the western. This may prove to be the correct view, and then the eastern form 
should be called C. diogenes Girard, and the western possibly C. obesws Hagen. 
I have not taken this course in the systematic part, since our knowledge of C. dio- 
genes is by no means complete. I know only the conditions in this state, but the 
eastern range of this species extends over large parts of the coastal plain, while the 
western occupies a vast territory reaching to the Rocky Mountains and the Gulf. 
It is also not impossible (although improbable) that the eastern and western areas 
are connected somewhere, (in Virginia’). Before this question is finally settled, and 
before we know more about the conditions under which C. diogenes occurs in the 
extralimital parts, it is best to refrain from expressing a positive opinion. Never- 
theless it is quite possible that there is a tendency in diogenes to split into varie- 
ties and species. A variety has been distinguished in Louisiana. 
We see that in certain forms my studies have led to a positive decision as to their 
taxonomic position. In other cases my observations must be completed and sup- 
plemented by additional evidence to be gathered in other parts of this country before 
a final opinion can be reached. The fault is not with the material at hand, but 
with the insufficiency of our knowledge of the extralimital parts. 
As to variations, that is to say, occasional aberrations from the typical form, we 
have seen that such are extremely rare among the Pennsylvania crawtishes, and 
have in most cases the character of freaks. Some of them, however, are interesting 
from certain points of view. 
No variations were discovered among one hundred and nineteen individuals of 
C. limosus. With reference to C. propinquus in Erie and Crawford Counties, I have 
pointed out that there is a certain amount of variation in the development of the 
§3De Vries (1905, p. 127) talks of ‘‘an old rule in systematic botany, that no form is to be constituted a species 
upon the basis of a single character.’’ This rule is entirely unknown to me in botany as well as in zodlogy. 
