The skull of Erethistes pussilus is described in detail. The general disposition of the bones corresponds to the siluroid pattern. Among the siluroid fishes, E. pussilus approaches the advanced forms in certain features such as obliteration of myodomic space, edentulous palate, absence of entopterygoids and supratemporals, intimate sutural articulation of posttemporals and complex vertebra with the cranium, diminished cranial cavity and loss of sutural articulation among the palatopterygoquadrate elements. In certain characters like the hyomandibula exclusively supported from the sphenotic, solitary hypohyal on each hyoid cornu, absence of interhyals, reduced orbits, edentulous vomer, small gape of mouth, toothless ectopterygoid and in the small number of branchiostegals, E. pussilus stands specialized alone among the catfishes. A diagnosis of the salient cranial characters of the fish is given and its relationship discussed.