1a - Maxillae without dentition;	Other extant siluriforms
1b –Maxillae toothed;	Family Diplomystidae	(2)
2 –Long and continuous lateral line; maxilla with two rows of teeth anteromedially, one row posterolaterally; with 8 to less than 20 maxillary teeth (8–19); loss of a separate cartilaginous pelvic radial;	Genus Diplomystes	(3)
2b –Lateral line interrupted, divided in two sections; maxilla with more than two rows of teeth anteromedial, two or more rows posterolaterally; with more than 20 maxillary teeth;	Olivaichthys viedmensis
3a –Skin of head, body, and fins densely covered with long, fine, “hairy” papillae; pectoral fin with posterior margin acuminate;	Diplomystes chilensis
3b –Skin with granulose aspect, with rounded papillae; pectoral fin with posterior margin rounded;		(4)
4a –Short and round papillae densely distributed all over the body; straight posterior margin of pelvic fins; posterior margin of pelvic fins near anal fin origin; urogenital pore and anus placed between pelvic fins in large individuals (ca. 150 mm SL and above);	Diplomystes camposensis
4b –Round and short papillae sparsely distributed on head, body and fins; posterior margins of pelvic fins rounded; posterior margin of pelvic fins broadly separated from anal fin origin; urogenital pore and anus in between posterior tips of pelvic fins and anal fin (ca. 150 mm SL and above);	Diplomystes nahuelbutaensis
4c –Round, long papillae densely covering head, body, and fins (verrucose or blackberry-like skin dimpled surface); high dorsal fin (20% of SL; range 17–25%), triangularly-shaped; urogenital pore and anus placed between posterior tips of pelvic fins;	Diplomystes incognitus sp. nov.