Revision of Trechus 
31 
extrinsically isolated in inescapable cave systems). Applying Emerson’s 
(1945) “practical” definition of a species, one could readily consider the 
taxa here treated as polytypic 77 schwarzi, T. vandykei, 77 tennesseensis, and 
77 aduncus as 11 or so distinct species because they are probably 
genetically (extrinsically) isolated from each other at the present time. 
However, intergradation between 77 hydropicus avus and 77 h. beutenmuellen 
(Barr 1962:73) provides a morphological yardstick against which these 
allopatric taxa can be compared. Polytypic 77 luculentus occurs at such low 
elevations that existing gaps ought to pose no problems to occasional gene 
flow between component subspecies. In most instances I have employed a 
conservative treatment; if I have erred on the conservative side, I will at 
least have indicated the close relationship of the taxa involved. For exam- 
ple, all of the aduncus- group taxa ( = polytypic 77 aduncus in the present 
paper) have, in my judgment, been derived from a single ancestral form 
which became isolated relatively recently by the gradual restriction of 
suitably cool, moist microhabitats to the summits of various mountain 
ranges in the Great Balsams, Cowees, and Nantahalas. Perhaps 77 
aduncus aduncus and 77 toxawayi may occasionally interbreed at some inter- 
mediate geographic point, but 77 howellae and 77 coweensis are probably 
absolute genetic isolates at the present time. My views on the probable 
degree of isolation at present are indicated in the taxon accounts, so that 
the reader may either accept my basically conservative interpretations or 
superimpose equivocally feasible, more liberal interpretations of his own. 
The addition of several new taxa has necessitated rewriting a key to 
species and subspecies of Appalachian Trechus. All known species and 
subspecies from the states of Georgia, Kentucky, Maryland, North 
Carolina, South Carolina, Tennessee, Virginia, and West Virginia are in- 
cluded. The present key makes greater use of external morphology than 
my 1962 key, but determinations should always be checked by examina- 
tion of an aedeagus where possible (cf. figs. 1-27 in Barr 1962, and figs. 
18-43 in the present paper). The range of most species and subspecies is 
quite limited, and the precise provenance of a specimen, if known, can be 
used to limit still further the species under consideration. 
The accounts of taxa other than those newly described take the form 
of an annotated checklist; the minimal information given is full tax- 
onomic citation and geographic range. Miscellaneous collecting informa- 
tion and data on syntopic and sympatric relationships with other species 
of the genus have been added when available. 
