Couplet 153

153a:  Fore coxal cavity narrowly closed; fore and mid coxae strongly transverse; mandible tucked into cavity when closed, not visible from side; antenna with 9 antennomeres, last 5 forming club; pronotum not grooved or carinate on disc; small beetles, < 2 mm long (Orthoperus)

Corylophidae   p. 434

153b:  Fore coxal cavity narrowly to widely open; fore and mid coxae circular to slightly transverse; mandible visible from side; antenna with 8-11 antennomeres, if clubbed, club of 1-3 antennomeres; pronotum usually with submarginal grooves or carinae, especially basally
(Figure 26-59C); size 1-10 mm, if < 2mm and lacking grooves or carinae on pronotum (Eidoreus), then antenna with 10-11 antennomeres, 1 or 2 of which form a distinct club