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Mesosoma attached to the gaster with a single, distinct segment (the petiole), the segment being set off by a distinct constriction in front and either a distinct constriction (Fig. a) or a shallow impression (Fig. b) behind
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Mesosoma attached to the gaster with two segments (the petiole and postpetiole), each segment being set off by distinct constrictions (Fig. aa)
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