10 BULLETIN 45, UNITED STATES NATIONAL MUSEUM. 



the teguliT', autl tlie ovipositor issues far anterior to the tip of the abdo- 

 men, reposing" in a ventral slit or groove, while the sheaths are ahvays 

 distinctly separated, never conjoined. 



Other families in the terebrant Hymenoptera agree with the Proc- 

 totrypidfii in having the pronotum extending back to the tegula?; but 

 in these, except in the family Pelecinida^, which I now believe, with 

 Haliday, Cresson, 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 iu a few cases, 2-jointed trochanters and in venational and an- 

 tenna] characters. All aculeate Hymenoptera, except in a few cases, 

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

 while in the Proctotrypida^ such is not the case: either both sexes have 

 the same number of joints or a less or greater number in the opposite 

 sex. 



With these few preliminary 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 description of the external 

 structure, biology, and classification. 



EXTERNAL STRUCTURAL CHARACTERS.' 



THE HEAD. 



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

 oblong, transverse,quadrate, or globular, and is rarely cornuted((7rt?e.s»-S'). 

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

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

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

 frequently margined, the margin often extending along the cheeks 

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

 ously arranged, their ])osition affording excellent secondary generic 

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

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

 or oval, ami most fre(|uently convex; in the wingless forms they are 

 occasionally very small bnt raiely entirely Avanting {Isohr<(cliii(m 9 ). 

 The clypeus is small or inconspicuous, and has afforded but slight 

 assistance in systematic work, although possibly more use could be 

 made of it. In tlie lU'thylina' it is strongly carinated medially. 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 usnally only in the males that the antenme are longer 

 than the body, and in this sex they are generally filiform or setaceous, 

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



' Details figured on plate i. 



