The harpaphine xystodesmid milliped genus Isaphe, characterized by two
telopodal branches and a prefemoral process that angles across the me
dial face of the telopodite, comprises two species. Isaphe convexa Coo
k occurs in montane forests of northern Idaho and Montana, and I. ters
a (Cook) is known from riparian woodlands in canyons of the Snake, Sal
mon, and Palouse river basins in southeastern Washington and west-cent
ral Idaho. They are distinguished by the degree of dorsal convexity, s
trong in I. convexa and weak in I. tersa, and by the length of the pre
femoral process, which is long and slender and extends well beyond the
caudal margin of the telopodite stem in I. convexa, and is short and
broad and terminates well before the margin in I. tersa. The strong co
nvexity in I. convexa results from greater expression of the dorsal cu
rvature than is the case in most xystodesmids because of a lower than
usual origin of the paranota, rather than from depression of the latte
r. The following new synonymies are proposed: Hybaphe Cook under Isaph
e Cook, H. curtipes Cook under I. tersa, and Leptodesmus (Isaphe) simp
lex Chamberlin under Harpaphe haydeniana haydeniana (Wood). Modern des
criptions are provided for the genus and species, and anatomical illus
trations and a distribution map are presented.