346 HYMENOPTERA OF AMERICA. [PART I. 



Bess. a. cliff. — This is a very difficult species. The yellow 

 margin of the 2d segment is rather bi-emarginate as in 0. mys- 

 tecus. — The body is not fulvo-velutinous as in Huastecus and 

 Olomilus, but mure black, with silky argenteous reflections; the 

 metathorax is not rough as in Otomitus, nor so widely excavated. 

 — It differs also from Huadecus, by its acute prothoraeic angles 

 and smaller size, its deeper and more rounded metathoracic 

 cavity, the yellow margins of abdomen, especially the 2d, wider; 

 the 1st being much narrower, and its feet black. It can be easily 

 distinguished by the wide margin of 2d segment. Sometimes, 

 especially in the males, the head, prothorax, and first segment are 

 almost wholly black. 



Bab. Mexico. This was caught in the temperate district of 

 Cuernavaca, south of Mexico, by my companion, H. Peyrot, to 

 whom it is dedicated; ? £ also have been taken near Orizaba, 

 4 ?, 2 £ (Sumichrast). 



d. Prothorax quite yellow above. Scutel and post-scutel yellow. 



142. O. collimbaris Sauss. — Niger; metathoracis foveola submar- 

 giuata ; abdominis 2' segmenti margine subreflexo ; clypeo 9 superne, 

 puncto frontali, oculari et post-oculari, flavis ; scapo subtus flavo ; 

 pronoto, macula subalari, scutello, post-scutello, metathoracis canthis, 

 abdominis segmentorum limbo, tibiisque antice, flavis ; alis subkyalinis, 

 costa sublerruginea, apice griseo ; tegulis ferrugineis. £ . 



Odyn. columbaris Sauss. Et. Vesp., I, 158, 42; pi. xvii, fig. 3 (1852). 

 Hab. South America,; Columbia, (type in the Paris Museum.) 



3. Body elongate, slender ; the abdomen especially, very slender. 

 Metathorax convex, having no longer a distinct excavation, 

 but sooner parted by a large groove, which separates its 

 two cheeks, somewhat as in Eumenes. Abdomen slender, 

 spindle-shaped; the first segment elongate, funnel-shaped, 

 sometimes subpedunculate. 



(Group of O. Totonacus.) 



These insects are all small, shining, not velutinous; black, with 

 luteous ornaments. They have quite the same appearance as 

 those of Section III (see below), but the scutel is black, the pro- 

 thorax has its hinder margin bordered with pale colors, and the 

 post-scutel is not truncate. 



