Key to species of Platygonia (modified from Young 1977)

1. Each forewing with four large yellow spots (two on clavus and two on corium) (Figs 7–8) ............. ................................................................................................... P. undecimmaculata (Fowler, 1899)

– Forewing without above color pattern .............................................................................................. 2

2. Each forewing with two broad white to pale yellow complete transverse stripes, one at basal third and another just behind claval apex ................................................................. P. zea (Distant, 1908)

– Forewing without above color pattern .............................................................................................. 3

3. Aedeagus, in lateral view, with a ventral process ............................................................................. 5

– Aedeagus, in lateral view, without a ventral process ........................................................................ 4

4. Aedeagus, in lateral view, gradually tapered apically .................................. P. infulata Young, 1977

– Aedeagus, in lateral view, obliquely truncate apically ............................. P. ignifera (Walker, 1851)

5. Crown-face transition without carina. Ventral process of aedeagus located apically (Southeastern Brazil) .......................................................................................................... P. angrana Young, 1977

– Crown-face transition with carina. Ventral process of aedeagus located on median third or more basally (Central America, Colombia, and Northern Brazil) ............................................................. 6

6. Pronotum with a large yellow spot; forewing with a large yellow spot extending from costal margin to median portion of clavus and a large orange spot at apical portion of corium, including anteapical cells .................................................................................................... P. praestantior (Fowler, 1899)

– Without the above combination of color features ............................................................................. 7

7. Disk of crown convex before ocelli ............................................................... P. detecta Young, 1977

– Disk of crown concave or depressed before ocelli ........................................................................... 8

8. Crown dark brown to black only at lateral margins .............................. P. spatulata (Signoret, 1854)

– Crown almost entirely dark brown to black (Figs 1–2) ............................................ P. nigra sp. nov.