Key to species of Acanthocephala Laporte in America north of Mexico

(Figs. 1–4)

1. Metatibiae broadly dilated for almost entire length, ending abruptly near apex (Figs. 5–8)............................ 2

1'. Metatibiae broadly dilated in basal 1/2, gradually narrowing beyond middle toward apex (Figs. 9–12).................. 3

2. Humeral angle of pronotum broadly rounded (Fig. 1), strongly extended laterally, elevated in posterior view (Fig. 13); metatibial expansions as in Figs. 5–6 .................................................................... A. declivis

2'. Humeral angles of pronotum more narrowly rounded, moderately extended laterally (Fig. 4), horizontal to slightly declivent in posterior view (Fig. 14); metatibial expansions as in Figs. 7–8 .......................................... A. thomasi

3. Metafemora of both sexes slightly expanded toward apex (occasionally parallel-sided or narrowed apically in males); both sexes lacking darkened areas beneath metacoxae on abdominal sternum 3 (second visible); antennal segment 4 red to yellow; metatibial expansions as in Figs. 9–10 ............................................................ A. terminalis

3'. Metafemora of males strongly incrassate, widest at middle, those of females slightly expanded; both sexes often with darkened areas beneath metacoxae on abdominal sternum 3; antennal segment 4 varying from concolorous with proximal segments to yellowish; metatibial expansion as in Figs. 11–12 ................................................... A. femorata .....................................................................................................