EUMENES. 61 



Among certain species, the thorax becomes narrow, lengthened, 

 compressed, and the metathorax is sometimes lengthened, so that 

 the resemblance to the Polybia increases. Although the Pachy- 

 menes present a series of forms coi-responding to those which one 

 sees among the Polybia; yet one can easily distinguish them from 

 these social insects by their truncate or bidentate clypeus, which 

 is not angularly terminated by a sort of tooth. 1 



This group is not as yet well studied; most of its species, 

 which appear to be rather numerous, are only known by rare 

 specimens scattered about in collections which have much simi- 

 larity among themselves, all having a silky body and colors pale 

 or variable, so that one can easily confound them. 



Unfortunately it is impossible for me here to establish good 

 differential characters between these insects, from only knowing 

 some of them by unique specimens and not having under my eyes 

 the types of all species heretofore described. 



I established the genus Pachymenes in the monography of 

 solitary wasps to receive those JEumenes of which the clypeus is 

 bidentate, the abdomen depressed, and of which the smooth and 

 satin-like body recalls the appearance of Polybia. But I have 

 now renounced this section, so difficult to define, although includ- 

 ing insects of a very peculiar appearance; for since that time I 

 have found many American Eumenes having the clypeus biden- 

 tate at the end, while certain Pachymenes have a bidentate 

 petiole, which destroys one of the differences on which the genus 

 Pachymenes was founded. I have, therefore, undertaken to 

 reduce the consideration of this generic group to that of a sim- 

 ple division of genera, and this division itself goes over into the 

 division Omicron so that it is impossible to fix a refined limit 

 between them. (Ex. E. Santa-Anna goes over to division Omi- 

 cron and is quite close to E. leevis.) 



1. Form rather lengthened ; thorax longer than wide ; abdomen 

 hardly depressed, the 2d segment not campanular. 



A. Petiole campanular, enlarged above beyond the middle, 



1 In my Monographic des Guepes Solitaires, I have confounded certain 

 species of Polybia described by Fabricius with the Pachymenes. See 

 Vespides, III, p. 153. (On the line before the last of that page, for chry- 

 sothorux, read pallipes.') 



