330 MEMOIRS OF THE CARNEGIE MUSEUM 



Tribe III. Sphegigaderini. 

 The species falling in this tribe are easily recognized by the much longer and 

 more slender marginal vein. They differ from the others also in habits, the majority 

 of the species being parasites of dipterous insects, and especially of the gall-making 

 species belonging principally to the family Cecidomyiidce. 



TABLE OF GENERA. 



1. Females 2 



Males ' 16 



2. Abdominal petiole longer than the hind coxse 3 



Abdominal petiole shorter than the hind coxae, or at least never longer 7 



3. Head with the cheeks compressed, the vertex not very narrow 4 



Head sublenticular, the cheeks rounded, the vertex narrow. 



Pronotum large, quadrate, meson otum flat, with complete parapsidal furrows ; second abdomi- 

 nal segment very large, occupying fully two thirds of the whole surface of the abdomen, the 

 following very short Syntomopus Walker (type S. thoracicus Walk.). 



4. Mesothoracic furrows incomplete, abbreviated posteriorly or only distinct anteriorly 5 



Mesothoracic furrows complete, distinct. 



Scutellum with a cross-furrow before the apex ; abdomen short oval, keeled beneath, the second 

 and third segments very large, the second broadly emarginate at apical margin. 



Merismus Walker (type M. megapterus Walk.). 



Scutellum convex, ivitlwut a cross-furrow before the apex, the second segment large, occupying 

 a little more than half the whole surface of the abdomen, the apical margin straight, not 

 emarginate Acroclisis Forster (type A. nigricornis Forst.). 



5. Metanotum usually smooth, but always with a median carina (except sometimes in Polycyrtus), the lateral 



folds also usually present 6 



Metanotum punctate, xvithoid either a median carina or lateral folds. 



Scutellunx convex, without a cross-furrow before the apex ; abdomen with the second and third 

 segments very large ; sometimes the abdomen is triangulate as in Perilampus. 



Trigonogastra Ashmead, g. nov. (type T. aurata Ashm.). 



6. Scutellum with a delicate cross-furrow before the apex ; abdomen with the second and third segments 



very large, the latter about one third the length of the second Sphegigaster Spiuola 



(type S. pallicornis Spin.). 



Scutellum without a cross-furrow before the apex or the furrow is subabsolute ; abdomen with the 



second segment very large, occupying half or a little more than half the whole surface, the following 



very short, often retracted Cryptoprymna Forster (type Prosodes atra Walker). 



7. Mesothoracic furrows incomplete, much abbreviated, or indicated only anteriorly 8 



Mesothoracic furrows complete, distinct, rarely only two thirds the length of the mesonotum 13 



8. Metanotum not broad, and with a more or less distinct median carina, or at least the carina is indicated 



basally 9 



Metanotum broad, jiunctate, without a median carina ? genus. 



9. Second abdominal segment at apex broadly and usually deeply, semicircularly emarginate 10 



Second abdominal segment at apex not broadly and deeply emarginate, straight or at the most with 



only a slight sinus 11 



