10 BULLETIN 45, UNITED STATES NATIONAL MUSEUM. 



the tegulti! autl the ovipo.sitor issues far anterior to the tip of the abdo- 

 men, reposing^ ill a ventral slit or groove, while the slieathsare always 

 distiiu'tly 8eparate<l, never conjoined. 



Other families in the terebrant llynienoptera agree with the Proc- 

 totrypidie in having the pronotnni extending baek to the tegula'; but 

 in these, except in the family I'elecinida', which I now believe, with 

 Haliday, Cvesson, and Cameron, is closely related to this family, the 

 ovipositor does not issue from the tip of the abdomen ; besides, other 

 good structural characters exist that readily separate them. 



From the families of the Aculeata they are separated by having, ex- 

 cept in a few cases, li-jointed trochanters and in venational and an- 

 tennal characters. All aculeate Ilymenoptera, excei>t in a few cases, 

 have the antenna? 12-jointed in the female and 13-Jointed in the male, 

 while in the Proctotiypida' such is not the case: either both sexes have 

 the same number of joints or a less or greater niind)er in the opposite 

 sex. 



With these few iireliminary remarks, and before entering into the 

 systematic description of the divisions, genera, .and species, I have 

 thought it advisable to go more fully into a (lescrii>ti(>n of the external 

 structure, biology, and classification. 



EXTERNAL STKUCTT'RAL ('lEARACTEKS.' 



TllK IlKAI). 



The head, in shape, is variable in the different groups; it may be 

 oblong, tran8verse,quatlrate, or globular, and is rarely cornuted ( (ralesHft). 

 The vertex is usually convex or subconvex and in only two genera, 

 Bryinus and Oonatopus, is it concave. The occiput is more or less 

 concave or excavated, with the superior margin rounded or sharp, and 

 frequently margined, the margin often extending along the cheeks 

 {Seelio, etc.). The ocelli when present are three in number and vari- 

 ously arranged, their position affording excellent secondary generic 

 characters; they are absent only in a few apterous forms in the differ- 

 ent group>. The eyes are usually of moderate size, rounded, ovate, 

 or oval, and most frequently convex; in the wingless forms they are 

 occasionally very small but raiely entirely Avanting [Isohrachium 9 ). 

 The clypeus is smnll or inconspieiious, and has afl'orded but slight 

 assistance in systematic work, although possibly more use could be 

 made of it. In the IJethyliuie it is strongly carinated medi.iUy. The 

 antenna' vary in length, shape, and in the number of joints from 7 to 

 15; also in the position of insertion. They may be elbowed or straight, 

 seldom exhibit a ring joint, and are of i»rimary importance in classifi- 

 cation. It is usually only in the males that the antennse .ire hniger 

 than the body, and in this sex they .are gener.ally filiform or setaceous, 

 more rarely clavate or subclavate, raiely branched or ramose, and 



> Details figured on plate i. 



