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Length.-The measurement from the front to the apical margin of the second segment of the gaster. Lateral angles of the clypeus.-The angle produced by the meeting of the apical and lateral margins of the clypeus. Pronotal lobes.-Lobes which project from either side of the prothorax into the mesoepisternum a short distance below the tegulae. Metanotum.-The simple transverse plate which bears the hind wings. This is the postscutellum of many authors. Propodeum.-The tergite of the first abdominal segment which has been fused to the thorax. Gaster.-The abdominal segments after the constriction separating them from the thorax, that is, all of the abdominal segments except the propodeum. Petiole.-The first segment of the gaster, or the first abdominal segment of many authors. It is not considered advisable to designate the petiole as distinct from the gaster and preceding it, for with the majority of the species of this family there is no petiole. Apical cordon of the petiole.-The salient margin or rim at the apex of the tergite of the petiole. Dorsal angle of the second segment of the gaster.-The median dorsal line when viewed laterally forms a more or less distinct angle which ordinarily marks the maximum inflation of the segment. Lateral angle of the second segment of the gaster.-The lateral lines when viewed dorsally form a more or less distinct angle as does the dorsal line, which ordinarily marks the maximum lateral inflation of the segment. The writer wishes to thank Mr. S. A. Rohwer for testing the keys to species and for criticisms and suggestions throughout the course of the studies herein presented. 345 by guest on June 5, 2016 http://aesa.oxfordjournals.org/ Downloaded from Annals Entomological Society of America [Vol. X ,The: genera i Éumenes ¡ a.ná.Zet.hus,ave not closely related, yet because of a superficial resemblance they .can, be conveniently considered together. They may be readily separated from all other wasps.of the family Eumenidae, found in America north of Mexico, by the first segment of the gaster which is petiolate, while in all other genera found Within these limits it is sessile of' subsessile.' In turn these two genera may bé separated by the following contrasting characters: • Eumenes.-Mandibles long," and,sharp pointed; clypeus as long or longer than wide; head compressed transversely, riot dilated behind the 'eyes,' posterior face truncate; thorax quadrate, not'strongly contracted anteriorly; prothorax. nearly> as»wide'as the head; petiole expanded, or at least.not strongly contracted apically; second-segment of the gaster sessile or subsessile.. f Zethus.-Mandibles short, obliquely truncated; clypeus wider than long; head dilated behind the eyes, posterior face emarginate; thorax strongly contracted before the' tegulai; prothorax much narrower than the head; petiole strongly Contracted apically; second" segment of the gaster subpetiolate.' .• Genus Eumenes Latrielle.The genus Eurrienes as it is "found in America north of Mexico forms a very homogeneous group. The differences of groups ...