Couplet 51

51a:  Antenna with 4 apical antennomeres expanded into asymmetrical club, first shining, other 3 tomentose (covered with densely matted woolly hairs) (Figure 26-6A); elytra usually with some combination of black and orange, but occasionally black (Figure 26-25B); fifth tergite with pair of longitudinal carinae (a ridge or keel) topped by stridulatory files; > 12 mm long, usually more than 15 mm (Nicrophorinae)

Silphidae   p. 408   (See footnote on p.383)

51b:  Antenna not as in preceding entry; fifth tergite without stridulatory files; color variable; length 13 mm or less, usually < 10 mm