Key to the Nearctic
Genera of the Erotylidae

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Fourth tarsomere scarcely reduced (pentamerous), subequal to third and attached in normal manner to end of third (fig.2); apical palpomere of maxillary palp cylindrical, not transverse or triangular; mentum strongly transverse (fig.4) 3
Fourth tarsal tarsomere strongly reduced (pseudotetramerous), not more than half length or width of third, attached mediodorsally to third (fig.3); apical palpomere of maxillary palp strongly transverse or triangular; mentum not transverse (fig.5,6) 2

Figure 2.
Tetramerous tarsus.

Figure 3.
Pseudotetramerous tarsus.

Figure 4.
Megalodacne sp.

Figure 5.
Tritoma sp.

Figure 6.
Triplax sp.

Elytra non-striate, confusely punctate with large black punctures; prothorax at base but little more than half as wide as greatest common elytral width; size large, 12 mm or more in length (Erotylinae) Gibbifer
Elytra regularly striate-punctate; prothorax at base subequal to greatest common elytral width; size small, 8 mm or less in length (Tritominae) 5

Large forms, 9 mm or more in length; black, elytra bearing two reddish fasciae; body largely impunctate (Megalodacninae) Megalodacne
Small forms, 6 mm or less in length; elytra without fasciae; body distinctly punctate (Dacninae) 4

Mesosternum extremely short and transverse, about ten times wider than long; prosternum bearing raised, triangular plateau which almost attains prosternal apex; elytron red with black spots Microsternus
Mesosternum not more than three times as wide as long; prosternum without such plateau; elytra black or brow, frequently with orange spots Dacne

Pronotal angle pores large and conspicuous, umbilicate (fig.7); apical palpomere of maxillary palp bearing distinct brush at apex (fig.6) 6
Pronotal angle pores small, inconspicuous, simple (fig.8); apical palpomere of maxillary palp without apical brush, postmandibular lobes poorly developed, usually not visible 7

Figure 6.
Triplax sp.

Figure 7.
Triplax sp., large pore

Figure 8.
Tritoma sp., small pore

Apical palpomere of maxillary palp strongly transverse; body without dorsal pubescence Triplax
Apical palpomere of maxillary palp squared, not transverse; body strongly punctured and pubescent Hirsutotriplax

Pronotum and elytra bicolored, bearing complex black pattern on lighter background Ischyrus
Pronotum unicolored, elytra unicolored or black with basal red spots 8

Prosternal lines long, either incurved anteriorly or meeting at prosternal apex (fig. 5); elytron immarginate basally; body relatively broadly oval or egg-shaped 9
Prosternal lines short, not or scarcely extending in front of inner coxal edges (as in fig. 6); elytron often margined basally; body elongate-elliptical 10

Figure 5.
Tritoma sp.

Figure 6.
Triplax sp.

Eyes coarsely faceted, relatively large and protuberant (fig.9) Pseudischyrus
Eyes finely faceted, relatively small (fig.10) Tritoma

Figure 9.
Tritoma sp.

Figure 10.
Pseudischyrus sp.

Head and pronotum reddish yellow to bright orange-red Mycotretus
Head and pronotum entirely black Haematochiton