106 . NYSSONIDE. 
slightly increasing towards the apex, inserted at the base of 
the clypeus but not approximate,—the scape thickest, elongate, 
obconic, the second joint very small, also obconic, the third 
scarcely longer, attenuated at its base, the remainder sub- 
equal and subcylindrical; the clypeus transverse, its anterior 
margin rounded, inflexed at the centre, which gives it the 
appearance of being emarginate, which is increased by a small 
process on each side, most conspicuous in the ¢, and having a 
short tubercle in the centre of its base, prolonged in some 
species into a longitudinal carina, and in the ¢ generally pro- 
jecting in an aquiline form; dabrum concealed; mandibles 
slightly arcuate, acuminate, and having a subdentate process 
towards the base of the interior. The tHorax rotundate; 
the collar linear, transverse ; the scutellum transverse, lunulate, 
having on each side below its posterior margin an incurved 
squama, which in some species is not separated, but forms a 
bifid plate; the metathorax truncated, with a mucro at its 
base, frequently obtuse, sometimes emarginate at its apex, 
and canaliculated above, generally resembling the lip of a 
vessel; the superior mings nith a narrow marginal cell slightly 
appendiculated, and one submarginal cell confluent with the second 
discoidal and recewing the single recurrent nervure ; the legs 
moderately long and stout; the anterior tars? strongly ciliated, 
and the intermediate and posterior tibice spinose, the bifid claws 
having a large pulvillus within their fork. The aspomENn 
ovato-conic, subtruncate at its base; the margins of the seg- 
ments somewhat constricted ; the apical segment acute in the 
9, and obtuse in the ¢. 
Type, O. lineatus. 
+4-+ This genus, the name of which is doubtlessly from 
o£) BeAos, in reference either to the acuteness of its sting or 
the velocity of its flight, was established by Latreille, in his 
Précis, in 1796. It is one of the genera which, for the 
want of specimens, I am unable to determine the distinction 
