346 Annals Entomological Society of America [Vol. X, 



The genera Eumenes and Zethus are 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 Eumenidaj, 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 

 or subsessile. In turn these two genera may be separated by 

 the following contrasting characters: 



Eumenes. — Mandibles long, and sharp pointed; cly]3eus as lon<^ or 

 longer than ^^^de; head compressed transversely, not dilated behind 

 the eyes, posterior face truncate; thorax quadrate, not strongly con- 

 tracted anteriorly; prothorax nearly as mde as the head; petiole ex- 

 panded, or at least not strongly contracted apically; second segment 

 of the gaster sessile or subsessile. 



Zethus. — Mandibles short, obliquely tnmcatcd; clypcus wider than 

 long; head dilated behind the eyes, posterior face emarginate; thorax 

 strongly contracted before the tegula;; prothorax much narrower than 

 the head; petiole strongly contracted apically; second segment of the 

 gaster subpetiolate. 



Genus Eumenes Latrielle. 



The genus Eumenes as it is found in America north of 

 Mexico forms a very homogeneous group. The differences of 

 groups of species, however constant they may be, do not justify 

 its division into subgenera, and it is probable that if extra- 

 limit al species were studied that many of these group differences 

 would disappear. However to facilitate the determination 

 of species, those under consideration may be divided into four 

 species groups, which named after the oldest species in each 

 group are as follows: The smithii group, the crucifera group, the 

 fraternus group,, and the crassicornis group. All of these except 

 the crucifera group would fall into Saussure's division Alpha. 



Key to the Species of Eumenes. 



1. Dorsum of the petiole impunctate bollii Cresson 



Dorsum of the petiole distinctly punctate 2 



2. Head flattened dorsally; petiole linear pj^riform, without abrupt inflation, 



ventral aspect of the tergite sparselj^ punctate bninneus Isely 



Head convex dorsally; petiole pyriform or campanulate, inflation always 

 more or less abrupt; ventral aspect of the tergite densely and coarsely 

 punctate 3 



3. Stemite of the petiole not distinctly separated from the tergite except near 



the apex; dorsal line of the second segment of the gaster strongly 



curved forward before the dorsal angle 4 



Sternite of the petiole distinctly separated from the tergite by a groove 

 and a carina; the dorsal line before the dorsal angle on the second 

 segment of the gaster not strongly curved forward 6 



