Key to the species of Cathorops from the Pacific Coast of Central and South America

1. 37–40 gill rakers on first and second arches; distance between anterior nostrils 6.92–7.14% SL; distance between posterior nostrils 8.19–8.51% SL .......................................................... Cathorops hypophthalmus

- 13–22 gill rakers on first and second arches; distance between anterior nostrils 3.60–5.98% SL; distance between posterior nostrils 4.23–7.26% SL .................................................................................................. 2

2. Medial groove of neurocranium very narrow and shallow, with irregular margins all its length.................. ......................................................................................................................................... Cathorops fuerthii

- Medial groove of neurocranium deep and large, with lateral margins regular and progressively narrower posteriorly .................................................................................................................................................. 3

3. 19–23 anal fin rays....................................................................................................................................... 4

- 24–27 anal fin rays....................................................................................................................................... 6

4. Vomerine tooth plates present; osseous bridge formed by lateral ethmoid and frontal granulated in all its length .................................................................................................................... Cathorops dasycephalus

- Vomerine tooth plates absent; osseous bridge formed by lateral ethmoid and frontal without granulation. ..................................................................................................................................................................... 5

5. 19–20 anal fin rays; accessory tooth plates with very large molariform teeth; dentary with a well pronounced posterior projection and very large and numerous molariform teeth on posterior portion ............. ............................................................................................................................................. Cathorops tuyra

- 22–23 anal fin rays; accessory tooth plates with molariform teeth of moderate size; dentary with moderately pronounced posterior projection and small and few molariform teeth on posterior portion ................ ................................................................................................................................ Cathorops steindachneri

6. Maxillary barbel 22.9–27.7% SL; 16–19 gill rakers on first arch; pectoral fin spine 16.9–18.7% SL; dorsal fin spine longer than pectoral fin spine ................................................................... Cathorops multiradiatus

- Maxillary barbel 28.4–38.2% SL; 13–16 gill rakers on first arch; pectoral fin spine 18.5–22.5% SL; dorsal fin spine shorter than pectoral fin spine .................................................................. Cathorops manglarensis