30 
Thomas C. Barr, Jr. 
all the rest of North America. New distributional records are given for 8 
taxa, yet no less than 12 taxa are still known from single collections at 
single sites, suggesting that yet further field investigations and revisions 
may be necessary before this large and interesting group of small moun- 
tain beetles is properly understood from a purely taxonomic point of view. 
There seems no special need to divide the Appalachian species of sub- 
genus Trechus (males with first two protarsomeres dentate and setose 
beneath) into two species groups, and I have lumped my “ carolinae group” 
(Barr 1962:73) with the hydropicus group. The great majority of the species 
belong to the endemic subgenus Microtrechus Jeannel, distinguished by 
having only the first, instead of the first two protarsomeres dentate and 
setose beneath in the male. This subgenus occurs in southwestern North 
Carolina and adjacent parts of Tennessee, Georgia, and South Carolina. 
Three distinctive species groups recognized by Barr (1962) have been 
retained in the present revision, although I have shifted one species (77 
verus Barr) from the uncifer group to the nebulosus group. In general, the 
species of Trechus reflect the major biogeographic features of carabid dis- 
tribution in the southern Appalachians as detailed by Barr (1969). Sub- 
genus Trechus has most of its species north of Asheville and north of the 
French Broad River valley, while the species of subgenus Microtrechus oc- 
cur south of the French Broad, although T. (T.) schwarzi and T. (M.) 
vandykei each have subspecies in the Black Mountains and on Pisgah 
Ledge, respectively. Various species and subspecies are endemic to most 
of the major mountain ranges of the area; lists of endemics by ranges are 
presented below, and locations of the ranges are shown in figure 46. 
The history of Trechus speciation in the southern Appalachians has 
presumably involved vertical expansions and contractions of taxon ranges 
in response to the colder, wetter climates of Pleistocene glacial maxima 
alternating with warmer, drier regimes of interglacial periods (Barr 1962, 
1969). For cold-limited species, suitable microhabitat areas waxed and 
waned as did the continental glaciers, with the elevation of the maximum 
permissible isotherm rising and falling like the level of the sea, from which 
the cool, wet summits of the mountains emerged like islands or 
achipelagoes. Because most Trechus species are cold-limited, their specia- 
tion patterns are essentially insular, and vicar species and subspecies are 
common. 
It is thus not surprising that in the southern Appalachians we encoun- 
ter arrays of closely similar taxa strung out along the major mountain 
chains like beads on a string. For some of the altitudinally limited taxa, 
the choice of assignment to the species or subspecies category is arbitrary: 
should another glacial maximum ensue, these taxa which are today 
allopatric could be brought together again (unlike their trechine cousins 
