ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 50 1 



no douljl 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 simihir, so that it is hard to tell them apart. But I think I am 

 able to do so. The differences are very slight, but I never observed intermediate 

 forms, and their e.xistence 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 ditference 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 (iirard, and the western possibly C. obesm 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 ( Julf 

 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 kn(jw more about the conditions under which C. diogenof 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 C. 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 tiiuir 

 taxonomic position. In other cases my oljservations 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 IkiihI, l)Ut 

 with tlie insufficiency of our knowledge of the extralimital parts. 



As to variation.^, tliat is to say, occasional aberrations from the typical form, we 

 have seen that such are extremely rare among the Pennsylvania crawfishes, 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. limosm. With reference to C. propivijKus in Erie and Cmwford Counties, I have 

 pointed out that there is a certain amount of variation in the development of the 



s^De Vries (1905, p. 127) talks of "an old rule in systenintic botany, tlint no form is to he constituted n sprcica 

 upon the basis of a single character." This rule is entirely unknown to me in botany as well as in roology. 



