Invertebrate Cave Fauna 
145 
probable center of distribution for species of Litocampa in the United 
States. Of the 20 species currently recognized from the United States, 17 
occur in the greater Appalachian region, and their combined ranges 
form a distributional track from the Interior Low Plateaus to the 
Appalachian Valley and Ridge (see Ferguson 1981a: Fig. 43). 
Of the six species of Litocampa in the study area, only two have 
narrowly circumscribed ranges that coincide with isolated exposures of 
limestone. The other species have wider ranges, although all except L. 
cookei, whose range extends as far west as central Kentucky and middle 
Tennessee, have relatively localized ranges confined to the study area or 
its periphery. The extensive distribution of L. cookei, the largest of any 
troglobitic dipluran in North America, is puzzling. Its distribution is not 
contiguous, however, but occurs in five disjunct clusters (Ferguson 
1981a: Fig. 43). Ferguson (1981a) has studied the morphology of this 
species in detail and has concluded that it may represent a complex of 
allopatric sibling species. 
Two final points should be made with respect to the origin of 
terrestrial troglobites. (1) The geographic distributions of four genera — 
viz., Kleptochthonius (Chamber lino chthonius), Litocampa, Pseuda- 
nophthalmus, and Pseudotremia — represented collectively by numerous 
troglobites in the study area are nearly congruent and together form a 
strong generalized distributional track that extends across the Ap- 
palachian Plateau. The importance of generalized tracks in biogeographic 
analysis has been reviewed by Wiley (1981). Such tracks may be used to 
estimate the range of ancestral species in monophyletic groups with 
similar distributions. 
The possibility suggested by Barr (1981a) that ancestors of 
troglobitic species of Pseudanophthalmus originated in the forest floors 
of the Appalachian Plateau in late Cenozoic times, with subsequent 
thrusts into limestone areas on either side, was discussed above. The 
coincident distributions of Kleptochthonius (Chamber lino chthonius), 
Litocampa, and Pseudotremia suggest a similar place of origin and 
center of distribution for ancestors of troglobites in these groups as well. 
Shear (1972) alluded to the possibility that Pseudotremia originated in 
the southern Appalachian Mountains through evolution from a proto- 
Pseudotremia stock in the Cenozoic. Similarly, Ferguson (1981a) 
suggested that the southern Appalachians might have been the center of 
distribution for North American species of Litocampa. The generalized 
track formed by these taxa tends to support these ideas and points to 
the central and southern parts of the Appalachian Plateau as an 
important geographic center for the distribution of ancestors of terrestrial 
troglobites in the Appalachian Valley, Interior Low Plateaus, and 
limestone areas on the eastern and western sides of the Appalachian 
Plateau. 
