134 Mr. R. C. L. Perkins' 



31. (32) Second sef^inent beneath largely but lightly impressed 



behind the costie ; above, greatly raised into a conical 

 tuberculate form 0. drumedaniit>, Blackb. 



32. (31) Second segment beneath with a distinct wide depression, very 



deep at its base, or else it is hardly more than simply con- 

 vex above, not raised into a conical or tuberculiite form. 



33. (34) Second segment beneath with the depression very deep at 



the base, above subtuberculately elevated ; abdomen 

 entirely black 0. melanognathvs, P. 



34. (33) Second segment beneath with a shallow or moderate 



depression ; above simply convex, not tiiberculately 

 elevated ; abdomen often yellow-banded or densely 

 clothed with decumbent grey pubescence. 



35. (36) Clypeus with one or two yellow spots (sometimes very 



small) ; depression of second ventral segment extremely 

 shallow, sometimes hardly perceptible. 



0. nervelli, sp. no v. 



36. (35) Clypeus without yellow spots ; depression of second ventral 



segment distinct, moderate. 



37. (38) Mesothorax and scutellum with appressed sericeous 



pubescence, so dense as to nearly conceal the surface, 

 impunctate or very obscurely punctured. 



0. sociabilis, P. 



38. (37) Mesothorax less densely clothed and more strongly 



punctured, the .scutellum with sparse and feeble, but 

 evident, punctures 0. scoriacens, P. 



39. (30) Clypeus truncate or somewhat emarginate at apex, never 



very deeply so, often impressed at apex behind the 

 emarginatiou, which gives it an appearance of being 

 deeper than is really the case. 



40. (41) Abdomen with two yellow bands and the second ventral 



segment Hat behind the costic without a depression. 



0. cooki, P. 



41. (40) Abdomen sometimes with one, very rarely with two, yellow 



bands ; if yellow-banded there is a distinct depression 

 behind the cost;e. 



42. (43) Mesothorax very densely rugulosely punctured, the 



punctures not coarse nor deep, running into one another; 

 (propodeum dull and smooth, at most a little rugose or 

 with some obscure punctures ; mandibles dark). 



0. venatui; P. 



43. (42) Mesothorax not very densely rugulosely pimctured (pro- 



jjodoum in some species <'(mspicuously rugose and in 

 some the mandibles are red). 



