HARRIS : CRAYFISHES GENUS CAMBARUS. 357 



two species are found. A collector starting at the head waters 

 of Squaw Run [37, 1] would find bartonii; following the stream, 

 he would soon notice robustus among his captures ; then an oc- 

 casional propinquus, till finally bartonii would become more rare 

 and disappear, and near the mouth of the creek he would find 

 only the species 'propinquus. If the collector chose to follow on 

 down the Alleghany river he would still notice only propinquus. 

 After reaching the Ohio, a few specimens from the ripples about 

 Neville island would show him that he had found another 

 species, rusticus." 



Under the "Summary of Habits" reference was made to the 

 * ' Conclusions Concerning Distribution ' ' for a discussion of char- 

 acter of localities. Crayfishes are found in varied habitats, from 

 burrows in a prairie which is dry for a large part of the year, 

 stagnant ponds, roadside ditches, and salt marshes, to the pure 

 cold water of mountain springs and streams. The differences 

 between the stream which has reached or nearly reached base 

 level and one which is in a younger stage of its life-history, or 

 between the upper and lower portions of a stream which shows 

 many stages of an ideal life-history, are well known and need 

 not be described here. Certain fishes are known to be typical 

 of each class of locality, and it is safe to assume that the rule 

 will to some extent hold good with the crayfishes as well. For 

 some species it is already known and field observation will 

 doubtless show it to be true of others. It is not advisable to 

 attempt a list of forms at present, but much may be learned in 

 regard to any species by consulting the table of distribution by 

 states and especially by river systems. 



One cannot work in the limited literature on the habits and 

 distribution of the different forms without observing that the 

 same species may be recorded as occurring in, or even typical 

 of, very different conditions of environment. As I have pointed 

 out, C. virilis is found in small streams, occurring almost exclu- 

 sively in the rocky, more rapid portions, and being absent in 

 the muddier, slower portions, though it may be found in very 

 muddy streams or even in stagnant ponds with C. immunis and 

 0. gracilis, where it must have the same habits. C. bartonii 

 seems to be characteristic of the cooler, purer mountain springs 

 and streams and is found in caves with C. pelhicidus, but it 

 is also found associated with C. diogenes, and with the same 



