ART. 16 NORTH AMERICAN ICHNEUMON-FLIES CUSHMAN 41 



MESOSTENU3 THORACICUS Cresson 



Fig. 3/, 4b, Gf 



Mesostcnus thoradcus Cresson, Proc. Ent. S«)C. Pliila., vol. 3, 1864, p. 314, 



female, male. — Provanciier, Nat. Can., vol. 7, 1875, p. 2(i(>; Nat. Can., vol. 



11, 1879, p. 113, fl.c:. 2h; Faune Ent. Can. Hym., 1883, p. 340, fls?. Sryh.— 



ViERECK, Smith, Ins. of N. J., 1910, p. 630. 

 Mesoatenns erythrogaster Ashmead, Proc. U. S. Nat. Mus., vol. 12, 1890, p. 406, 



male. Tijite. — Cat. No. 2017, U.S.N.M. (new synonymy). 

 Mesostenidca (Mesostenidea) thoracica (Cresson) Viereck, Hym. Conn. (1916), 



1917, p. 329. 



Within its range the most abundant Mesostenine. 



Discussion based on tyjDe and homotype (Cushman), the type of 

 erythrogaster and many other specimens in the National Collection. 



Feiiude. — Length, 8-13 mm. 



Slender ; temples strongly, obliquely narrowed, nearly flat, polished 

 and sparsely punctate; vertex and frons medially rugulose; eyes 

 parallel, practically straight within; face medially somewhat ele- 

 vated and densely punctate, orbits coriaceous and sparsely punctate ; 

 clypeus strongly convex, with a narrow reflexed margin, shining and 

 sparsel}'^ punctate; malar space two-thirds basal width of mandible; 

 mandible stout, teeth subequal ; basal joints of flagellum slender, suc- 

 cessively slightly shorter, fourth three-fourths as long as third, others 

 successively gradually shorter. Thorax nearly twice as long as deep 

 and distinctly deeper than broad, densely punctate with some stria- 

 tion in pronotal and mesopleural impressions, and scutellum polished 

 and impunctate ; notauli finely f oveolate, meeting in a median impres- 

 sion ; propodeum more or less rugose on posterior face, apical carina 

 broadly interrupted medially, high on angles. Abdomen less than 

 a half longer than head and thorax, finely, coriaceous, postpetiole 

 polished with scattered punctures, suture between tergite and sternite 

 obsolete; second tergite much longer than broad at base rather 

 densely punctate, third more finely and sparsely punctate; sheath 

 nearly as long as abdomen ; ovipositor in profile stout, deeper at apex 

 than at base. 



Head black with orbits (usually interrupted behind top of eye), 

 face medially (sometimes entirely), clypeus at base, mandibles partly, 

 and an annulus centering on flagellar joint 8 whitish. Prothorax and 

 dorsum of mesothorax and metathorax and sometimes the anterior 

 portion of mesopleuruin, sternum and propodeum black with whitish 

 markings as follows : Collar and humeral margin of pronotum, tegu- 

 lae, subalar tubercles, median spot on mesoscutum, scutellum laterally 

 and apically and its basal carinae, and postscutellum ; thorax and 

 propodeum otherwise ferruginous with upper part of prepectus and 

 apical slope of propodeum sometimes paler; legs testaceous, front 

 coxa and trochanter, spot on upper side of middle coxa, and hind 



