Key to species of Lethierium

1. Metope smooth, without distinct intermediate carinae (Figs 3, 8, 11, 14). Each forewing with distinct shoulder-shaped prominence (or knee prominence) well visible in dorsal view (Figs 1, 6, 9, 12).......................................... 2

- Metope with distinct median and sublateral carinae (Figs 18, 53). Forewings with weak knee prominences (Fig. 16). Morocco ................................................................................... L. carinatum sp. nov.

2. Hind tibia with a single lateral spine...................................................................... 3

- Hind tibia with two lateral spines......................................................................... 4

3. Phallobase basement with large lobe-shaped processes (Fig. 26). Aedeagus with nearly straight ventral hooks. Algeria .................................................................................... L. reiberi (Lethierry, 1878)

- Phallobase basement with short lobe-shaped processes (Fig. 34). Aedeagus with strongly curved ventral hooks. Algeria and Morocco ....................................................................... L. juniperi (Bergevin, 1915)

4. Metope with straight upper margin (Fig. 14). Male anal tube with a rounded process on its lateral margins (Fig. 47). Lobes of phallobase basement enlarged apically (Fig. 49). Style with weakly concave hind margin (Fig. 51). Morocco ............................................................................................... L. grandilobum sp. nov.

- Metope with weakly concave upper margin (Figs 11, 39). Male anal tube without process on its lateral margins (Fig. 41). Lobes of phallobase basement narrowing apically (Fig. 46). Style with deeply concave hind margin (Fig. 43). Morocco ....................................................................................... L. cedricolum (Dlabola, 1989)