The genus Isonychus contains about 60 described species, largely from Central and South America. None have been recorded previously from the United States. The species described below from southern Arizona extends the known range of the genus about six or seven hundred miles northward.

The genus is placed in the Macrodactylini and may be briefly characterized as follows: surfaces of vertex, pronotum, scutellum, and elytra covered with setae; elytra feebly striate; setal color pattern usually present on elytra; fore tibia bidentate; all tarsi with two claws, each of the latter cleft at tip and with a small basal tooth; one tibial spur on each fore leg, two spurs on each mesothoracic leg in both sexes and two tibial spurs on each metathoracic leg of the female, spurs lacking or single on the metathoracic legs of the male; fore and middle coxae contiguous or very narrowly separated.