NORTH AMERICAN HYMENOPTERA. 135 



anteriorly the mesosternum, and in some species entirely absent, 

 epimerum mesopleuralis separated from the episternum by a strong, 

 generally foveolated furrow, armed with a strong crest just anterior 

 to the ynedial coxit, which Is sometimes represented simply by a small 

 pointed prominence (groups veatralis and hilaris), or is absent 

 (groups pinguis to pedicellatus incl.) ; middle segment marked by a 

 longitudinal central furrow and usually by a curved one which en- 

 closes its upper surface, posterior face with or without a lateral ridge, 

 sides flat or depressed, divided sometimes by a medial, longitudinal 

 furrow. Legs in female simple, never very strongly spinose, in the 

 male subject to great variation, the fore trochanters being sometimes 

 spined, the fore femora simple, dentate at base beneath, armed with 

 a long spine beneath between base and middle, or flattened and 

 dilated basally, fore tibise simple, or bearing a large vari-shaped 

 shield as in groups temdglossus and largior, fore tarsi simple, flat- 

 tened, dilated, or distorted (group largior) ; medial tibiae with one 

 spur, first joint of medial tarsi simple, or having a peculiar form 

 and its length variable ; hind tarsi simple, the first joint, ho\vever, 

 varying in length in some cases ; anterior wings consisting of a 

 median, submedian, a marginal, one cubital (submarginal) and 

 two discoidal cells, costal cell closed, the second dixcoidal is generally 

 much shorter tJuin the first, although in some groups is of the same 

 length ; hind wings with a median and submedian cell, the latter 

 being much shorter than the former. Abdomen elongate, convex 

 above and beneath; segments even, or contracted at base and apex 

 (group interriiptas), the first segment varying from petiolate to 

 almost sessile ; in the petiolate form it is longitudinally furrowed at 

 base, and in the more sessile forms with a strong basal depression, 

 which is bounded outwardly by a ridge ; female only with a pygidial 

 enclosure, except in one group (pinguis), the form of which varies — 

 sometimes broad, flat, again much contracted and deeply channeled ; 

 last dorsal segment of male with or without a medial furrow ; sculp- 

 ture very variable. 



1. Group interruptas. 

 The species of this group have the bodies, particularly the head 

 and thorax, very coarsely sculptured, being covered usually with 

 great, coarse punctures, which on the dorsulum, scutellum and meso- 

 pleurJB are often interspersed with strong strite and the sides of the 

 middle segment are usually coai-sely striated. The medial pr(tduced 



TRANS. AM. ENT. SOC. XXII. MAY, 1895. 



