no. 3602 CRAYFISHES — HOBBS, HOLT, AND WALTON 65 



Brancliiobdellid associates include B. illmninatus at stations 5, 22, 

 44, 86, 97, 121; C. branchiophila at 24, 86, 97; Cjallax at 3, 5, 24, 54, 

 61, 86, 95, 97; C heterognatha at 3-5, 24, 61, 64, 86, 97, 123; C holostoma 

 at 7, 11, 13, 21, 22, 37; C. ingens at 5, 54, 61, 64, 86, 95, 97; C. phila- 

 delphica at 3, 5, 9, 12, 21, 22, 24, 37, 44, 46, 53, 54, 60, 121, 123; P. 

 alcicornus at 3-5, 24, 61, 64, 86, 95, 97; and Xd. formosus at 21. 



Discussion 



Since the crayfishes in the area serve as hosts to the epizootic 

 ostracods and branchiobdellids and since, in this area, neither of the 

 latter is known to occur independently of their hosts, it seems highly 

 probable that they reached the Mountain Lake region on one or more 

 of the crayfish stocks. If this likelihood can be accepted, a knowledge 

 of the probable origin of the crayfish fauna may help to explain, in 

 part, some of the associations that have been recorded above. 



One of the crayfishes, Cambarus b. bartonii, is at home in the Appa- 

 lachian Mountain system, and probably had its origin in the southern 

 part, migrating in postglacial times as far north as New Brunswick, 

 Canada. This crayfish ascends the smallest headwater streams, 

 burrows in seepages, springs, and along water courses; furthermore, 

 it is not averse to leaving the aquatic habitat to crawl about on land. 

 These habits would, of course, enable it to ignore narrow terrestrial 

 barriers between headwater streams, and, consequently, it is not 

 surprising that it occurs in all three river systems in the Mountain 

 Lake Region. 



Cambarus sciotensis, a not-so-distant relative of C b. bartonii, 

 appears to be confined to the Ohio drainage system in the Kanawha 

 and Scioto tributaries, where it seeks cover beneath stones or in vege- 

 tation throughout most of the stream bed. Its range is not adequately 

 known, but it seems probable that it reached this area through 

 migrations up the Kanawha and New Rivers, and here it is confined 

 to the New River drainage. 



Cambarus I. longulus, probably the most primitive member of the 

 genus in the area, almost certainly has reached its present range by 

 the migration of its ancestors from the southwest (Coosa-Tennessee 

 drainage systems) leaving populations in the Tennessee (C. I. longi- 

 rostris Faxon) and New (C. I. chasmodactylus James) systems. The 

 typical subspecies is found in the lower mountains and Piedmont 

 provinces from the James River to the Yadkin River in Virginia and 

 North Carolina. Although perhaps exhibiting a larger number of 

 generalized characteristics than other members of the genus in the 

 area, it is almost as ecologically restricted as C. carolinus in that here 

 it is confined to riffles in tributaries of the James and Roanoke Rivers. 



The range of Cambarus acuminatus and its relatives forms an asym- 



