Oligosarcus

1. Lateral line with 47 to 54 pored scales; head length contained 2.9 to 3.5 times in standard length; dentary the same size or shorter than upper jaw................ O. paranensis

1’. Lateral line with 36 to 40 pored scales; head length contained 3.7 to 3.8 in standard length; dentary much longer than upper jaw.............................................. O. pintoi