14 HYMENOPTERA OF AMERICA. [PART I. 



Abdomen pediculate; the first segment in the form of a petiole, 

 linear at its base, next inflated, and finally more or less con- 

 tracted at its extremity, which renders the inflation globular or 

 elliptical. The second segment, in form of a rounded bell, is 

 often pediculate. 



Sexual differences. — The males have the clypeus transverse, 

 quadrate, broad. Their antenna? are terminated either by a hook, 

 or by a spiral. 1 The females have the antennas simple and the 

 clypeus discoidal, ofteu convex or lozenge-shaped, transverse. 



Insects American. 



This genus is easily recognized by its peculiar face, its trans- 

 verse clypeus, large head, and the singular form of its abdomen. 12 



Among the Zethus the mandibles are quite short, overlapping 

 beneath the clypeus ; their triturating edge is terminal, not lateral 

 as among the Eumeninae. 



The size of the head is such that the eyes do not entirely 

 cover the cheeks. The metathorax has such variable forms that 

 it recalls what one sees in the Odynerus ; one can always here 

 distinguish two lateral ridges, which extend from the base of the 

 wing to the insertion of the petiole, as in certain Odynerus 

 (Hoplopus or Epipone). 



The petiole is quite variable. Its expansion produces a form 

 sometimes globular, sometimes more lengthened. The 2d abdomi- 

 nal segment, whether subsessile or long pediculate, has the form 

 of a bell or compressed oval. It is dilated suddenly (globularly), 

 or gradually (like a pear). Its posterior border always presents 

 two distinct foliations, the inferior projecting remarkably. This 



1 It is not possible to establish a definite limit between these two forms: 

 for often, with the hook, there also commences a spiral. When the spiral 

 is very distinct, the 13th article, in place of terminating in a point as when 

 it forms a hook, is lengthened, curved and obtuse. (See Saussure, Vespi- 

 des I, pi. ii, fig. 3, d.) 



2 The Zethus were mostly confounded with the Eumenes np to the time 

 when I reunited the species in one genus, of which the buccate characters 

 and the general form are too distinct to admit of any confusion. But I 

 could not entirely separate from the genus Eumenes, some species which 

 I had not seen, and of which, even as wasps, the descriptions were incom- 

 plete (E. riifinoda Lep. ; E. subslricta Hald., etc.). 





