Fossorial Hj/menoptera of North America. 391 



Mandibles rapidly narrowing towards the tip, tridentate, the middle 

 tooth largest. Thorax oblong, nearly twice as long as broad; prothorax 

 small, narrow; nieso-scutuin as long as broad, from a little in advance 

 of the middle the sides narrow towards the hind margin, being eon- 

 cave ; scutelhun short, sublimate. Enclosure of the propodeum very 

 linear ; posteriorly abruptly bent down a little before or near its mid- 

 dle, the surface above being flat, sub-triangular and bounded by a low 

 ridge ; flanks vertical, straight, somewhat convex, mesially below the 

 insertion of the wings, nearly as broad as long, a little more inclined 

 than the hind flanks ; coxoe rather small and short, middle and hind 

 trochanters long and slender. Primaries much as in Cemonus. The 

 2d costal is larger and more angulated. 1st sub-costal space is of the 

 same form as in Cemonus, but much longer. 2d sub-costal square, a 

 little longer than broad ; in the secondaries the sub-costal recurrent is 

 half way between the outer margin aud the origin of the sub-costal 

 uervure. Legs slender, fore femora smooth, with an inner row of long 

 hairs; 1st joint of the tarsi with a thin row of slender spines; hind 

 legs with scattered long light hairs ; 1st joint nearly as long as the 

 remainder, shorter by the length of the 4th joint, all the joints are 

 thickly spined within. Abdomen acute ovate, pedicelled. pedicel two- 

 thirds as long as the breadth of the abdomen. 



This genus differs not only in the neuration, but in the square pa- 

 rallel sides of the head, in the clypeal region not being clearly defined 

 and covered with silvery pile, while the anteuna? are placed nearer 

 together. 



In this genus the propodeum is larger and much lengthened ; en- 

 closure with no smooth spaces, but covered with a net-work of fossas; 

 posteriorly much produced beyond the enclosure. The 3d costal cell 

 is rather triangular, where in Cemonus it is oval, lanceolate; the 2d sub- 

 costal vein joins the sub-costal cell within the 3d medio-submedian re- 

 current, where in Cemonus it is either confluent with that nervule, or 

 goes beyond it to the main nervure. Pemphredon has a more cubical 

 head, a longer abdomen, and the species are of larger size than in 

 ( '< monus. 



Pemphredon concolor, Say. 



P. concolor, Say, Long's 2d Exp. A pp. p. 339. (1834). 



Cemonus concolor, Ilarr., Cat. Ins. Mass. p. 68. (1835). 



Pemphredon concolor. Smith, Cat. Kym. Br. Mus. iv. p. 426. (1856). 



P. morio, Cress., Proc, p. 486. (1S65). 



9 . A large specimen in the Harris collection I refer with some 

 doubt to this species, as the individual is evidently considerably larger 



