1864.] 315 



abruptly truncate behind, the elevated lines indistinct, the lateral tu- 

 bercles small and acute or subacute. Wings hyaline ; nervures and 

 stigma black, the latter with a pale spot at base ; areolet very minute, 

 quadrate. Legs yellowish-rufous, the four anterior coxae whitish, the 

 posterior tibiae sometimes obfuscated, their tarsi yellowish. Abdomen 

 elongate, subovate, shining, yellowish-rufous ; basal segment polished, 

 the apical third quadrate ; sometimes the terminal segment is tinged 

 with yellow ; ovipositor as long as the abdomen, rufo-piceous, valves 

 black. Length 4 — 5-j lines; expanse of wings (U — 8 lines. 



Male. — Resembles the female, but is more slender, the antennae are 

 rather longer than the body, the annulus distinct above, but indistinctly 

 defined beneath and yellowish ; the fice is entirely white ; the space 

 between the anterior and middle coxfe is also white; the extreme base 

 of the metathorax is blackish ; the four anterior coxfe and trochanters 

 are white, as well as the posterior tarsi, except extreme base and apex 

 which are black ; the extreme tips of the posterior femora and most of 

 their tibiae also black, and the apical segments of the abdomen are 

 sometimes obfuscated, pi-obably from discoloration. Length 4 lines ; 

 expanse of wings 7 lines. 



Hah. — X. Y. (Grote) ; Penn. (Cresson) ; Delaware (Dr. Wilson). 



This species is easily distinguished by its pale rufous color, with the 

 head and mesothorax black variegated with white lines. 



4. Mesostenus gracilis, a. sp. 



Pale yellowish-rufous ; head, antennse and mesothorax black, varied with 

 white: wings subhyaline, iridescent; metathorax unarmed. 



Male. — Pale yellowish-rufous, slender, shining; head black; the or- 

 bits, interrupted behind, a large spot on the face confluent with the 

 orbits, clypeus, most of mandibles, and the palpi, white; antennae long, 

 porrect, entirely black. Thorax shining; mesothorax black, the dorsal 

 lines deeply impressed ; pectus also black ; tegulse, a sutural line before 

 and a short line beneath the wings, and a line on the collar extending 

 down on each side of pectus, white ; anterior part of the pleura stained 

 with blackish and having an obscure whitish spot on each side between 

 the anterior and middle coxae ; scutelluni and postscutellum black, po- 

 lished, the former with its tip and lateral margins narrow white, ex- 

 tending forward upon the lateral carinas, in the shape of a V ; meta- 



