A new species of the psammophilous and brushlegged North American genus Amercaenis Provonsha and McCafferty, Amercaenis cusabo Provonsha and McCafferty, new species, is described from larvae taken from the Black River (North Carolina), the Pee Dee River (North Carolina), and the Savannah River (Georgia and South Carolina). The new species differs from the only other known species of the genus, A. ridens (McDunnough), for example, in having segments 2 and 3 of the labial palps subequal in length, and having the transverse row of setae on the forefemora consisting of long spatulate setae. Adults provisionally assigned to the new species are associated with the larvae morphologically and in locale do not fit any other adults of North American Caenidae, and differ from the congener A. ridens by dark dorsal coloration. The two species of Americaenis are biogeoraphically disjunct.