A new species of ground cricket in the genus Allonemobius (Hebard) is described from the southwestern United States. Like many singing Orthoptera, this species is morphologically cryptic and most easily distinguished from related species by using molecular characters and male calling song traits. We describe Allonemobius shalontaki as a new species and present data suggesting its reproductive isolation from congeneric species. Allonemobius shalontaki exhibits a unique male calling song and possesses a distinct allozyme genotype. Additionally, we present an electrophoretic key to the genus and propose phylogenetic relationships among species.