I9 o 5 .] ORTMAMN — AFFINITIES OF CAMBARUS. 129 



species, we do not know much about their habits, but a few remark- 

 able cases may be mentioned, (i) C. virilis and C. immuuis, 

 although sharply separated, are rather closely allied, and occupy 

 large identical tracts of the central states. We know that C. virilis 

 prefers running water with stony bottom, while C. immunis is a 

 pond and ditch form (see above, p. 117). (2)6". monongalensis 

 inhabits, in western Pennsylvania, almost the same territory that 

 is occupied by C. diogenes. The first, however, belongs to the 

 hills, the second to the lowlands (see Ortmann, Ann. Carnegie 

 Mus., v. 3, p. 400). 



The various drainage systems have a different effect upon the 

 species of the different subgenera, which is apparently due to funda- 

 mental differences in their habits. (1) Bartonius is preeminently a 

 mountain-stream group. It goes up into the smallest streams, up 

 to their very sources. In this region, changes of drainage, due to 

 piracy, are common, and rather the rule than the exception, and 

 thus the species quite generally occupy the headwaters of streams 

 running in different directions from the divides. This is exampled 

 by the distribution of the following species : extraneus, bartoni, 

 longulus, latimanus, carolinus, and probably also by diogenes. (See 

 Adams, " Migration of Divides," in Americ. Natural., 35, 1901, 

 p. 844). (2) The blandingi-section belongs originally to the low- 

 lands of ths Gulf and Atlantic plain. Here removal of barriers 

 largely has taken place, and thus the species of this group belong 

 to the drainages of different coast rivers, for instance : lecontei 

 blandingi, clarki, troglodytes, alleni. (See Adams, ibid., p. 842 : 

 "In a country approaching base-level a wide distribution of the 

 fauna will be facilitated.") (3) The subgenus Faxonius belongs 

 to the great rivers of the interior basin, and does not ascend far into 

 the headwaters, at least in the mountainous regions, and also does 

 not descend far toward the coastal plain. Consequently, the drain- 

 age systems being more permanent, the distribution of these species 

 is more closely connected with the latter. We may, perhaps, com- 

 pare this — in a very general way — with the period of maximum 

 roughness of Adams (/. c), although this does not hold good for 

 all of this immense region. Indeed, there are important excep- 

 tions, and the subgenus has crossed over into the lake-drainage 

 (C propinquus, obscurus, rusticus, virilis, immunis}, and evert into 

 the Hudson Bay drainage (C virilis). This has been brought 



