In the “The Pygidiidae, a family of South American Catfishes” (Mem. Carnegie Mus. VII, Sept. 1918, pp. 259—398, plates XXXVI—LVI, 39 text figures), I described and figured ninety-seven species of the Pygidiidae. They were relegated into six subfamilies, Nematogenyinae, Pygidiinae, Pareiodontinae, Stegophilinae, Vandelliinae, and Tridentinae. The most primitive of the genera is no doubt Nematogenys, (fig. 9) of north-central Chili. In it the maxillary is rudimentary and is continued as a barbel similar to that in the Nematognaths in general. The chin bears one pair of barbels. The opercle fig. 8 (18) and interopercle (17) are unarmed. In all the other genera mental barbels are lacking, there are normally two barbels at the end of the maxillary, and in all the known genera the opercle and interopercle are provided with spines or hooks.