492 MEMOIRS OF THE CARNEGIE MUSEUM 



C. obscurus, C. harfoni, C. vionongalensis, and C. diogenes. These are the species 

 found in Allegheny ( 'ounty, and they are most complete, since I had the best chance 

 to study them, three of them being found in the immediate vicinity of my residence 

 and the fourth (ohscnrus) within a few miles and within easy reacli. 



We are able to distinguish two main tjq^es of life-history, which I should like to 

 call for convenience the ivarm water and the cool wafer ti/pes. C. obscurns and 

 diogenes represent the first, and agree with each other in having well marked mating- 

 and spawning-seasons, and in early summer a period when no males of the first form 

 are found. They differ, however, in the fact that in C. obscums sexual maturity is 

 reached, as a rule, at the end of the first summer, wliich does not seem to be the 

 case in C. diogenes. Of the other species, of which no complete series of dates are at 

 hand, the river-species, C. liynosus, C. i'>ropinquus, and C. propinquus sanborni, very 

 likely agree with C. obscxims, for the comparison of the dates does not reveal any 

 differences. 



The coo! water type is represented by C. bartoni and C. monongalensis. Both are 

 characterized by the absence of well marked mating- and spawning-seasons. They 

 may be expected in any stage of development at any part of the year, even winter 

 making no exception. C. carolinas probably belongs also to this type, although the 

 observations are too scanty to jDOsitively establish the fact. 



One thing in conclusion should be especially emphasized. The life-history and 

 the habits of different species of the genus Cambarus are by no means similar. On 

 the contrary they differ considerably, and the difterences may be accounted for pri- 

 marily by the different ecological conditions under which they live. Consequently 

 it is inadmissible to generalize from facts observed in one species only, and further 

 it is to be expected, if other species are studied, that additional types of life-history 

 will be discovered. 



VI. ECONOMIC VALUE. 



1. Popidar Inioirledge of Crawfishes. 

 The crawfishes of this state are generally well known t(j the population. They 

 are abundant and large enough to attract the attention even of the casual observer. 

 Rut it is chiefiy the small boy who is interested in them. Three popular names are 

 employed for them, crab, craijjish, and craivfislt. "Crab" obviously is a misnomer, 

 belonging originally to the marine Brachgura, but it is largely in use all over the 

 state, and chiefly so in the cities. The word " crayfish " is used the least. In my 

 experience I heard it mostly in the mouths of such people as had a certain amuunt 

 of schooling and had acquired some knowledge of natural history. This word is 



