40 PROCEEDINGS OF THE NATIONAL MUSEUM tol. 74 



District of Columbia; Beltsville, Md., W. L. McAtee; Chesapeake 

 Beach, Md., A. Busck; Heckton Mills, Pa., W. S. Fisher and A. B. 

 Chamberlain ; Ocean Grove, N. J. ; and Long Island, N. Y. 



Genus MESOSTENUS Gravenhorst 



Mesostenus Gravenhorst, Ichn. Eur., vol. 2, 1829, p. 750. Genotype. — MesoHienus 

 transfuga Gravenhorst. 



Stenaraeus Thomson, Opuse. Ent., .fasc, 21, 1896, p. 2378. Genotype. — Meso- 

 stenus transfuga Gravenhorst. 



A group of slender, rather small species with clypeus convex 

 with a narrow reflexed margin ; eyes parallel within and not sinuate ; 

 malar space nearly or quite as long as basal width of mandible; oc- 

 cipital carina neither sinuate nor prominent below; frons trans- 

 versely swollen above with a median carina but without horns, the 

 carina sometimes, especially in males, simulating a horn but this high 

 up on frons; antennae slender; thorax elongate; scutellum moder- 

 ately convex, immargined ; notauli distinct and usually completely de- 

 fined; propodeum with both basal and apical carinae, the latter 

 usually obliterated medially, without distinct apophyses, spiracles 

 small oval; areolet long and narrow with recurrent shortly ante- 

 f ureal, rarely quadrate with recurrent interstitial, closed at apex; 

 nervulus interstitial or antef ureal; postnervulus broken at or below 

 the middle; nervellus broken far below middle, its upper abscissa 

 perpendicular to cubitella; legs slender, front tibia not at all in- 

 flated; hind trochanter with basal joint fully as long as apical; 

 abdomen narrow, petiole gradually merging into postpetiole, suture 

 between tergite and stemite frequently obsolete, sternite usually 

 extending beyond spiracles; ovipositor sheath at most as long as 

 abdomen. 



The five known North American species may be separated as 

 follows : 



1. Pleura and propodeum red 2 



Pleura and propodeiim black or black and yellow 3 



2. Apical carina in female very strong on angles ; in male strong throughout, the 



propodeum roughly reticulate-rugose behind ; ovipositor in profile broad at 

 apox ; hind tarsus in female paler than tibia, in male white except at 

 extreme base and apex ; antenna in male always with a distinct white 



annulus thoraciciis Cresson. 



Apical carina of propodeum in female not especially strong on angles, in male 

 frequently interrupted in middle and not especially strong, the propodeum 

 not reticulate-rugose behind; ovipositor in profile very narrow at apex; 

 hind tarsus in female not paler than tibia, in male rarely with more than 

 three middle joints white, frequently all black; antennae in male rarely 

 with distinct white annulus gracilis Cresson, 



3. Thorax profusely marked with yellow leucopns Ashmead. 



Thorax not profusely marked with yellow 4 



4. Temples narrowed ; abdomen not black at apex promptus Cresson. 



Temples as broad as eyes or nearly ; abdomen broadly black at apex. 



melanurus, new species. 



