Key to species of Platydoras .

1. Sides without light midlateral stripe; midlateral scutes very shallow, depth of 10 th scute 7.2-9.8% of SL; coastal drainages of Suriname and French Guiana … Platydoras costatus

1’. Sides with light midlateral stripe; midlateral scutes shallow to deep, depth of 10 th scute 8.8-17.8% of SL………………2

2. Light midlateral stripe usually punctated with small dark spots in axils of few (anteriorly) to all midlateral thorns (except in some specimens from Negro drainage); eye relatively large, horizontal diameter of adipose eyelid usually>59% (range 56.1-88.9%) of interorbital width; upper Orinoco, Negro, Essequibo and Demerara drainages……… ………………………………………… Platydorashancockii

2’. Light midlateral stripe solid, without dark spots; eye relatively small, horizontal diameter of adipose eyelid usually <59% (range 41.2-65.1%) of interorbital width……………3

3. Midlateral scutes shallow, depth of 10 th plate 8.8-11.9% of SL; midlateral scutes on caudal peduncle clearly separated by thin strip of skin from middorsal and midventral caudalpeduncle plates (i.e., modified procurrent caudal-fin rays); coastal drainages from Pindaré to Parnaíba rivers, northeastern Brazil ……………………… Platydoras brachylecis

3’. Midlateral scutes deep, depth of 10 th plate 12.0-16.6% of SL; midlateral scutes on caudal peduncle usually contacting, and often interdigitating with, middorsal and midventral plates (except some specimens from lower Amazon); lower Orinoco, Amazon and Paraguay-Paraná basins…… ………………………………………… Platydorasarmatulus