Andrognathus hoffmani, n. sp., is described from near Monterrey, Nuevo León, México, and is the second species of the genus to be discovered; A. corticarius Cope was named in 1869. Anatomical details of both species revealed through scanning electron microscopy are discussed. Contrary to the assertion of Gardner (1975) that the form of the gonopods in the Andrognathidae is of no taxonomic utility, we found striking differences between the two species discussed here, and differences between two populations of nominal A. corticarius. It is possible that A. corticarius as presently understood represents a complex of cryptic species.