32 (35) Second ventral segment behind the costae with a distinct 



impression, which is wide and shallow, or of moderate width 

 and depth and of triangular shape (clypeus of male deeply 

 or rather deeply emarginate). 



33 (34) Male with the scape entirely yellow in front; female with a 



yellow spot on each side of the propodeum near the insertion 

 of the abdomen. O. nauiarum. 



34 (33) Male with the scape black, female with the propodeum without 



yellow markings. O. erro, var. 



35 (32) Second ventral segment behind the costae generally flattened 



but without a triangular depression ; when there is a depres- 

 sion it is very narrow, linear or sublinear (clypeus of male 

 never deeply emarginate, but sometimes an apical impres- 

 sion gives it the appearance of having a deeper emargination 

 than really exists. 



36 (37) Second ventral segment of abdomen abruptly, but not greatly 



raised from the apices of the costae, depression feeble and 

 linear for the most part ; wings shining fuscous without blue 

 iridescence. O. waianaeanus. 



37 (36) Second ventral segment flatfish or slightly convex behind the 



costae, never abruptly raised from their apices, wings fre- 

 requently with blue iridescence. 



38 (39) Costae of second ventral segment very short, shorter than the 



tumid basal part of the segment anterior to them. 



O. acoelogaster. 

 39^ (38) Costae of second ventral segment not very short, the middle 

 ones generally long and not shorter than the basal division 

 of the segment. 



40 (41) Wings shining fuscovis, without distinct blue iridescence, 



clypeus and thorax entirely black (female vmknown). 



O. acyanus. 



41 (40) Wings dark, with more or less evident blue or steely iridescence 



clypeus of male nearly always and thorax often yellow- 

 marked. 



42 (43) Maxillary palpi of female very long and fringed with long 



hairs; male with the front of head rather remotely punc- 

 tured, maxillary palpi more developed. 



Pseudopterocheilus relictus. 



43 (42) Maxillary palpi of female normal; head closely punctate in 



front in the male and the palpi less developed. 



Odynerus lithophilus. 



44 (29) Abdomen not yellow-banded, rarely with the margins of some 



of the segments faintly and inconspicuously testaceous; 

 thorax not yellow-marked. 



45 (54) Wings dark, with distinct blue or purple iridescence. 



46 (51) Propodeum rugose or rugosely punctured; second ventral seg- 



ment with a wide shallow depression, and all the costae 

 well developed. 



