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Key to Megalomyrmex species known from Costa Rica

Workers:

10a. Mandibles with 5 distinct teeth, apical tooth largest, proximal tooth smaller, remaining three teeth the smallest and subequal in size (figure); Weber's Length greater than 1mm: 20

10b. Mandibles with a large apical tooth, a smaller proximal tooth, and a series of usually 4 or more denticles, these minute and difficult to see; if only 3 denticles (some specimens of drifti), then Weber's Length less than 1mm: 40

20a. Mandibles striate; occipital margin not visible in face view: Megalomyrmex modestus

20b. Mandibles largely smooth with large piligerous punctures; occipital margin visible in face view: 30

30a. Propodeal suture very deeply and broad; propodeum broadly curved, without differentiated dorsal and posterior faces; ventral margin of postpetiole protruding, evenly convex, without anteroventral spine: Megalomyrmex wallacei

30b. Propodeal suture less strongly impressed; propodeum with differentiated dorsal and posterior faces, and often with pair of tubercles; ventral margin of postpetiole flat, sloping anteriorly, anterior margin often terminating in long, needle-like spine: Megalomyrmex foreli

40a. Mandibles coarsely striate; color orange brown; body covered with dense, yellow pilosity: Megalomyrmex symmetochus

40b. Mandibles smooth; color and pilosity various: 50

50a. Eyes very small, less than 6 facets across greatest diameter; color yellow orange: 55

50b. Eyes larger; color usually red brown to black: 60

55a. Epipetiolar carina complete over the foramen; subpetiolar process with a transversly sculptured flange: Megalomyrmex miri

55b. Epipetiolar carina incomplete; subpetiolar process a laterally compressed tooth, not a transverse flange: Megalomyrmex wettereri

60a. Scapes do not or barely surpass vertex margin; mandible with three or four small teeth proximal to larger distal pair: Megalomyrmex drifti

60b. Scapes distinctly surpass vertex margin; mandible with five or more denticles proximal to distal pair: 70

70a. Mandibles with series of 12 or more minute denticles proximal to distal pair; median portion of clypeus protruding and the anterior margin of clypeus recessed, such that in face view the median portion of the clypeus partially obscures the anterior margin: Megalomyrmex silvestrii

70b. Mandibles with series of 7-10 denticles proximal to distal pair; clypeus not protruding, anteromedian margin visible in face view: 80

80a. Mandibles with basal margin rounding into masticatory margin, the two margins not sharply differentiated at an angular juncture; clypeus produced and subangular, not evenly convex; epipetiolar carina incomplete: Megalomyrmex JTL-003

80b. Mandibles subtriangular, with well-differentiated basal and masticatory margins; clypeus evenly convex; epipetiolar carina complete: Megalomyrmex mondabora

Page author: John T. Longino longinoj@evergreen.edu