At a glance this species is distinguished from all the other species of the genus Nyctinomus by the length of the metacarpal bone of the third and the fourth finger, by the peculiar manner in which the interfemoral membrane and the wings are attached to the tibiae, and by the very long end of the tail free from the membrane. Muzzle as in the other species; upper lip very expansible and thick, deeply grooved by vertical wrinkles.