GENERA OF HYMENOPTERA. 



Fig. 3. 



a, prothorax ; b, mesotborax ; c, 

 scutellum ; d, postscutellum ; e, meta- 

 thorax ; f, tegulae ; g, parapsidal 

 grooves. 



the impressed lines between the lobes, termed parapsidnl grooves or 

 furrows (g), are frequently used in characterizi .^ certain genera 



among the smaller Parasitica. The 

 scutellum (c) is generally flat, or aim- 

 pi) convex, sometimes square, or scu- 

 tatiform, or bituberculate, und occa- 

 sionally armed with spines or teeth ; 

 in the Ichneumonidie it is sometimes 

 pyramidal and often of difi'erent color 

 from the rest of the thorax. The }wst- 

 sciitellum (d) is almost always narrow 

 and inconspicuous, rarely armed with 

 a spine as in Oxyhelus. The metatho- 

 rax (e) is variously formed, generally 

 short and rounded posteriorly, some- 

 times elongate and truncate behind, 

 and occasionally bituberculate or bi- 

 spinose ; on each side towards the base 

 is placed a small spiracle, which is 

 either round, oval or linear; the Tenthredinidaj often exhibit two 

 very small white s]K)ts (cenchri) at the sides of the extreme basal 

 portion ; in the Ichneumonida? the metathorax is often more or less 

 distinctly areolated. The pleura or breast is the lateral portiim of 

 the thorax beneath the wings, and is very seldom referred to in char- 

 acterizing genera. 



The Wings (fig. 4, anterior ; fig. 5, posterior) are four in number, 

 naked, membranous and horizontal ; the anterior pair generally much 

 larger than the posterior, the extreme base of the former being pro- 

 tected by a scaly ])late, called the tegula (fig. 3, f); they are fur- 

 nished with veins or nervures, for the most part arranged longitudi- 

 nally and transversely (but never forming a close net-work as in the 

 Neuroptera), the spaces enclosed between the nervures are of various 

 sizes and shapes and are termed celh and are fully illustrated and 

 explained in the diagrams given below. In some families, e.g. Chal- 

 cididae and Proctotrupidfe, the number of these veins or nervures is, 

 however, liable to considerable reduction, the wings being almost, or 

 even entirely destitute of them and are often more or less pubescent. 

 In a genus of the last-named family the anterior wings are very long, 

 consisting of a linear branch, dilated and spatulate at tip and ciliate 

 with long hail's ; in another genus they are notched at the extremity. 



