Invertebrate Cave Fauna 
109 
Branch of the Potomac River actually constitutes an eighth drainage 
basin but has been excluded from our analysis because of its insignifi- 
cant size in the study area. The cave fauna of this basin was discussed 
previously by Holsinger et al. (1976). 
In the companion study on the cave invertebrates of West Virginia 
(Holsinger et al. 1976), we also divided that area into cave faunal units 
that corresponded to major drainage basins and discussed zoogeo- 
graphical relationships in a context similar to that of the present paper. 
Somewhat similar, but broader, faunal units than those recognized in 
the Virginias and northeastern Tennessee were distinguished for the 
regional cave faunas of the Interior Low Plateaus by Barr (1967a), 
northwestern Georgia by Holsinger and Peck (1971), and Illinois- 
southeastern Missouri by Peck and Lewis (1978). 
A list of the cave-limited species has been compiled for each basin 
or faunal unit (Tables 5-1 1). Although these lists are restricted primarily 
to troglobites, we have included a few select troglophiles that our obser- 
vations indicate are commonly represented by cave-restricted pop- 
ulations. 
1. Shenandoah Basin . — This faunal unit includes that part of the 
study area drained by the Shenandoah River and its tributaries and 
covers approximately 8328 km 2 (Fig. 2). It is defined by the Blue Ridge 
Mountains on the east, North and Shenandoah mountains on the west, 
the Virginia-West Virginia state line on the north, and a drainage divide 
(composed partly of carbonate rock) with the James River basin on the 
south. Outside the study area, the basin continues for a short distance 
through the extreme northeastern corner of West Virginia to a point 
where the Shenandoah River joins the Potomac River at Harpers Ferry. 
The regional terrain is generally rolling and is significantly punctu- 
ated only by Massanutten Mountain, a prominent ridge that partly 
divides the basin into two valleys for about half of its length. A total of 
396 caves are recorded from the basin in the study area; a majority are 
small, and only a few are of major extent. Although the area contains a 
fairly extensive exposure of carbonate rock (Cambrian to Devonian), 
much of it is dolomite and calcareous shale. As a result, the potential 
for extensive cave development has been greatly limited. The regional 
cavernicolous fauna contains 25 cave-limited species; 23 are troglobites, 
and 14 are endemic to the basin (Table 5). 
2. James Basin . — In the study area this faunal unit includes all of 
that part of west-central Virginia drained by the James River and its 
tributaries and covers approximately 7745 km 2 (Fig. 2). It is defined by 
the Blue Ridge Mountains on the east, Allegheny and Peters mountains 
on the west, drainage divides (with carbonate rocks) with the upper 
Potomac drainage system (i.e., South Branch and Shenandoah rivers) 
on the north, and drainage divides (also with carbonate rocks) with the 
