248 IIYMENOPTERA OF AMERICA. [PART I. 



f Superior face of metathorax produced behind thJ 



post-scutel. Stenodynerus. 



Superior face of metathorax not produced behind the 

 post-scutel. 



a. Truncate, with the post-scutel. j Pachodynerus. 



(. Odynerus. 



b. Truncate, without the post-scutel, which is not 



L truncate. Stenodynerus. 



f . _ , . f Odynerus. 



I Abdomen elongate, its base widely truncate. i ' , 



l- Stenodynerus. 



J f Pachudynerus. 



J Abdomen conical. i ^ , 



J t Odynerus. 



| Abdomen spindle-shaped, contracted at base, the first 



(_ segment funnel-shaped or cup-shaped. Stenodynerus. 



f First abdominal segment longer or as 



long as wide. Stenodynerus. 



-J First abd. segment having its superior 



r Pachodynerus. 

 [ face wider than long. < Odynerus. 



I Stenodynerus (by exception). 

 First abd. segment more strongly punc- 

 tured than the second. Stenodynerus. 

 First abd. segment not so strongly punc- 



f Pachodynerus. 

 1 tured as the second, smooth. < ~ 7 



(. Odynerus. 



First and second segments equally 



f Stenodynerus. ~\ .. „ 



L P^tured. XoaynL. } •"•P""**- 



The insects of this group have a marked tendency to become 

 rugose, and the border of the 2d abdominal segment is cribrose 

 with strong punctures ; in general, at any rate, it offers a zone, 

 rugose and a little impressed or channelled. 



But there is a set of species which offers, on the contrary, a 

 smooth, shining body, with a tendency to omit the punctures. 

 This type is represented here by the 0. bidens only, but is met 

 again in other genera. 



The species presenting a rugose body offer a great similarity 

 to the European species, and this similarity goes so far that one 

 might attempt to indicate with certainty among them the Euro- 

 pean type from which they seem to be derived. So, for example, 

 the 0. (Eh yji chin m) dorsale, derived from the Ehynchium ocu- 

 latum; the 0. foraminatus from the 0. simplex, etc., while those 

 having a smooth body which have been identified, are of a type 



