Key to US Stigmatomma species

Key to the species of Stigmatomma from the United States.

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1

 * Lobes of frontal carinae contiguous or fused. Small, length about 3 mm. Color yellowish. Known only from Arizona => Stigmatomma orizabanum
 * Lobes of frontal carinae separated by a distinct gap. Larger, length over 3 mm. Color blackish brown to reddish brown. Widespread => 2

2

 * Inner borders of mandible expanded near base, so that the blades are trianglular in shape. Large double teeth with rounded apices. Genal teeth reduced to inconspicuous obtuse angles. Head in frontal view without a tooth or sharp point on each side of head near mandible. Known only from North Carolina => Stigmatomma trigonignathum
 * Inner borders of mandibles straight to convex, not expanded near base, the blades linear. Large double teeth prominently acute. Genal teeth acute and projecting. Head in frontal view with a tooth or sharp point on each side of head near insertion of mandible => 3

3

 * Inner margins of mandibles and anterior clypeal margin straight in outline. British Columbia south to northern California => Stigmatomma oregonense
 * Inner margins of mandibles, and usually also the anterior clypeal margin, convex in outline. Temperate North America at least to Arizona => Stigmatomma pallipes