62 BULLETIN 15, UNITED STATES NATIONAL MUSEUM. 



MESITIUS .Spinola. 



Couipte. reu<Ui Ilym. de Para (1846); Mem. Acad. Turin, Ser. ii, torn 13 (1853); 

 Westw., Thes. Ent. Oxou., p. 222. 



(Type J/, f/hilioiii Spin.) 



Head oblong, siibcoiivex, not much longer than wide; eyes oval; 

 ocelli distinct. 



Antenna^, 13-jointed, in ^ long, in 9 much shorter, the scape thickened, 

 about four times as long as the pedicel, the following joints short. 



Maxillary palpi rather long, 6-jointed, the three basal Joints gradu- 

 ally increasing slightly in length, the three terminal ones longer and 

 sul)equal; maxilla terminates in three membraneous ciliated lobes; 

 labial palpi 3-jointed, the joints nearly equal. 



Mandibles oblong, with the a])ex oblique and but slightly sinuated; 

 in the 9 the outer tooth is small, acute, followed by a veiy small tooth, 

 the rest of the surface scarcely denticulate; in $ 4- or o-dentate. 



Thorax: Prothorax long, triangular or trapezoidal, the apex at the 

 junction Tsuth the head contracted, with a deep transverse furrow above; 

 mesonotum usually with two distinct furrows, often abbreviated poste- 

 riorly; scutellum with two fovea^ at base; metathorax with prominent 

 posterior angles, the dorsum with many longitudinal carina^. 



Front wings with a moderate sized stigma, a long, incomplete marginal 

 cell and two basal cells, the apices of both being more or less oblique. 



Abdomen ovate or oblong-ovate, smooth, the second vSegment the 

 longest, the apical margins sinuate or emarginate. 



Legs as in Epyris, the claws slender, nearly straight, with a tooth at 

 the middle. 



This genus closely resembles Epyris and great care is necessary to 

 distinguish it from that genus. As far as the North American species 

 are concerned I have had no diflBculty in separating them by the two fovece 

 at the base of the .scutellum. 



Westwood, in Thesaurus Entomologicus Oxoniensis, p. 2213, and in the 

 Transactions of the Eutomological Society of London, 1881, ]). 125, 

 states that the genera Isohrachium Forster (Hym. Stud., ii, p. 96, 1856) 

 and Heterocaiia Dahlbom (Hym. Europ., II, p. 21, 1854) are synony- 

 mous with Mcsitius, an oi)inion in which I can not concur. The apical 

 segments of the abdomen of Heterocoelia nigriventris Dahl., the type 

 of the genus, is figured by Dahlbom, loc. cit., p. 23, and it, as well as 

 the description, plainly point to a chrysidid. Dahlbom also figures it 

 on PI. I, Fig 15. A careful comparison of this figure with Westwood'S 

 (Thes., PI. 31, Fig. 10) plainly shows that Dahlbom has a genuine 

 chrysidid and Westwood a genuine pioctotrypid. 



It is inexplicable to me how so careful a worker as Westwood could 

 have made so grave an error. Forster, in his definition of the genus 

 Isobrachium^ evidently confused and correlated as sexes two distinct 

 insects. His Isohrachium dichotomus is a 9 , and evidently a genuine 



