492 MEMOIRS OF THE CARNEGIE MUSEUM 
C. obscurus, C. bartoni, C. monongalensis, and C. diogenes. These are the species 
found in Allegheny County, 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 (obsewrus) within a few miles and within easy reach. 
We are able to distinguish two main types of life-history, which I should like to 
call for convenience the warm water and the cool water types. ©. obscwrus and 
diogenes represent the first, and agree with each other in having well marked mating- 
and spawning-seasons, and in early summera period when no males of the first form 
are found. They differ, however, in the fact that in C. obscwrws sexual maturity is 
reached, as a rule, at the end of the first summer, which 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. limosus, C. propinquus, and C. propinquus sanborm, very 
likely agree with ©. obscwrus, for the comparison of the dates does not reveal any 
differences. 
The cool water type is represented by C. bartont 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. carolinus probably belongs also to this type, although the 
observations are too scanty to positively 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 differences 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. Popular knowledge of Crawfishes. 
The crawfishes of this state are generally well known to the population. They 
are abundant and large enough to attract the attention even of the casual observer. 
But it is chiefly the small boy who is interested in them. Three popular names are 
employed for them, crab, crayfish, and crawfish. ‘ Crab” obviously is a misnomer, 
belonging originally to the marine Brachywra, 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 amount 
of schooling and had acquired some knowledge of natural history. This word is 
