no. 3G02 CRAYFISHES — HOBBS, HOLT, AND WALTON 69 



known to occur on any other host. Also sharing the same host is 

 Dactylocythere chalaza, which, in contrast to Phymocythere phyma, was 

 derived from a stock that is primarily associated with lotic habitats but 

 which invaded the groundwater in adopting C. carolinus as a host; it 

 is not improbable that this crayfish brought the progenitors of Dt. 

 chalaza with it when it moved into the area. The third species 

 postulated to have arrived in the area from the southwest is Dt. 

 daphnioides, which, in the Mountain Lake region, is associated with 

 only one crayfish, C. sciotensis, but outside of the area (in the New, 

 Watauga, and Pound drainages) it infests several species, including 

 C. b. bartonii. The fourth species, Dt. falcata, insofar as is presently 

 known, has a discontinuous distribution and probably reached the 

 Roanoke River from the southwest, perhaps following the same route 

 as proposed for Dn. truncata in getting from the New into the Roanoke 

 basin. The perplexing problem of Dt. falcata not having been found 

 in the New River leads to speculation that it may have been routed by 

 other species there, perhaps one or more of its close relatives. 



Southeastern components of the entocytherine fauna of the region 

 include Entocythere internotalus, Dt. suteri, and An. ancyla. The 

 principal hosts of all three of these species are C. acuminatus and C. I. 

 longulus, and it is likely that C. acuminatus has been more important 

 in the dispersal of these three than has C. I. longulus, not only because 

 of its larger surface area and broader ecological tolerance, but also 

 because its range far exceeds that of the smaller species. In summary, 

 the presence of the ostracods in the Mountain Lake region may be 

 explained as follows: 



Ascetocythere asceta, Dactylocythere chalaza, Dt. daphnioides, and Dt. falcata — by 

 migrations from the southwest along the Tennessee and New drainage systems. 



Ankylocythere ancyla, Entocythere internotalus, and Dt. suteri — by migrations along 

 the Atlantic slope from the southeast. 



Donnaldsoncythere ardis, Dn. ileata, Dn. truncata, and Phymocythere phyma — 

 originated in or near the area. 



Donnaldsoncythere scalis — by migrations from the north into the James drainage. 



Entocythere kanawhaensis — from the west along the Kanawha and New rivers. 



Two-thirds of the branchiobdellids of the Mountain Lake area are 

 endemic to the southern Appalachians. Of the remainder, Xg. in- 

 stabilius is confined to mountain streams, at relatively high elevations 

 throughout the Appalachians, but it is indistinguishable from the 

 western Xg. oregonensis. The greater number of species of Xironogiton 

 are found to the west of the continental divide, and one must assume 

 that the present disjunct distribution of the genus is a relict of a former 

 continuous range. The monotypic Bdellodrilus illuminatus is widely 

 distributed over North America. At this time few inferences can be 

 drawn as to place of origin, migration routes, or evolution of this 



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