190 HTMENOPTERA OF AMERICA. [PART I. 



appendix, and on each side of the scntel is a distinct depression. 

 While in the true Ancistrocerus the post-scutel is nearly always 

 truncate posteriorly, having a posterior face (with rare excep- 

 tions), 1 in Stenodynerus it is not truncate out angulate posteriorly ; 

 the metathorax being produced a little beyond the post-scutel and 

 not so sharply truncate posteriorly, from which circumstance the 

 posterior angle of the post-scutel is not cut off. The posterior 

 plate of the metathorax never oners a basin regularly bordered 

 as in the true Ancistrocerus, and with spiniform angles. The 

 abdomen is in general strongly punctured; 2 the first segment 

 being also as much or more strongly punctured than those fi 

 ing. This segment is sometimes convex, rounded, at times divided 

 into two distinct faces by the suture as with the true Odynerus ; 

 but the superior face is often narrow and lengthened, not short 

 and wide as in the true Ancistrocerus. 



The suture is often placed at once on the declivity of the ante- 

 rior face of the first segment. It is subject to become indistinct, 

 so that one does not know whether to consider it as a suture or 

 a simple line of rugosities. Among certain species one perceives 

 a double rugose line and between the two lines a sort- of fluting, 

 so that the segment appears to have two sutural lines. 



The Stenancistrocerus have an appearance, which, when it is 

 known, permits one to distinguish them quite easily from the true 

 Ancistrocerus } the form being wider and more flattened. But 

 they resemble in so striking a manner certain Stenodynerus, that 

 one can confound them with these last, and there are very many 

 species of each group with forms so correspondent, that without 

 the presence or the absence of the suture at the base of the 

 abdomen, one would confound them specifically. (See the Ody- 

 nerus of the Division Stenodynerus.) 



In fine, I will indicate as an empirical guide, what may serve 

 to distinguish the Ancistrocerus, properly called, from the 

 Stenancistrocerus; in the first the band on the 1st abdominal 

 segment is in general either regular or widened on the sides, 

 while in the second it is either regular or retracted on the sides. 



1 Ancistrocerus cinguialus Cress. 



2 The species of South America, particularly those of Chili, often have 

 the abdomen feebly punctured. 



