214 HYMENOPTERA OF AMERICA. [PART I. 



black hair with which they are bristling, and by their exceptional 

 livery. They have the wing for the most part strongly reddened, 

 with the end of a brown-violet or entirely brownish ; the feet red 

 or black, often also the antennre, tegulae and the clypeus ?, red; 

 sometimes even the prothorax. Almost all carry some yellow- 

 white markings, and have two bands of the same color on the 

 abdomen. Among these insects the posterior face of the meta- 

 thorax is neither more smooth nor more rugose than the rest of 

 the thorax; it offers the same appearance, which is quite excep- 

 tional among the Odynerus. 



Very many of these Odynerus have at the base of the 2d seg- 

 ment beneath, a fold, which seen in profile, appears like a tubercle, 

 some specimens presenting even an acute tubercle. The clypeus 

 of the females is pyriform, truncate, or subemarginate at the end, 

 black or red. That of the males is narrow, lengthened, biden- 

 tate, and of a pale yellow color. 



The form also is generally very characteristic. The posterior 

 face of the metathorax is not shaped like that of a true Odynerus, 

 but in a sort of pentagon, growing larger from its inferior extremity 

 as far as the middle, where are the lateral angles, then finely re- 

 tracted as far as the post-scutel, forming with it somelatero-superior 

 ridges which converge from below upward (the post-scutel forming 

 the 5th side of the pentagon) ; here the posterior face of the 

 metathorax is generally triangular ; it widens as far as the sum- 

 mit and the marginal ridges, at which place they are distinct, 

 straight, and oblique, converging toward the bottom. There 

 remains then only the latero-inferior ridges of the metathorax. 

 (0. humeralis.) 



This conformation of the metathorax involves an analogous 

 configuration in the 1st abdominal segment, for this is always 

 such, that it in a manner conforms itself to the metathorax so 

 that it places, or exactly fits its anterior face against the posterior 

 face of the metathorax (and this results from the fact that the 

 two pieces are applied against each other during the period of 

 the metamorphosis so that they are in reality moulded against 

 each other). 



The first abdominal segment has also its anterior, face tri- 

 angular, and the depressed form of the abdomen causes the supe- 

 rior border of the triangle to be but a little arcuate. 



As the metathorax is quite vertically truncate, the first segment 



