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Mandibles long and straight, inserted in the middle of the front margin of the head, and with only 2 or 3 large teeth near the tips (Fig. a) (sometimes with small denticles along their inner margins, but these are much smaller than the teeth at the tips)
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Mandibles long and straight or triangular, inserted at the sides (lateral corners) of the head, and with the teeth either located along the entire inner margin (Fig. aa) or lacking
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