74 PR0CEEDIN08 OF THE NATIONAL MUSEUM. vol.39. 



the "postscutellum/' but this term is preoccupied by the postnotum 

 as used by most authors. 



The anterior mesonotal plate is the scuto-prescutum, though the 

 division into these two parts is often obscured. In most of the 

 Tenthredinoidea there is present a distinct prescutum (10, 16-19, 

 Psc^, separated by a V-shaped suture Qi) from the scutum (Sct^). A 

 similar prescutum is present also in some of the Ichneumonidae, such 

 as MegarJiyssa lunator (25, Psc^). In others, however, such as 

 Erymotylus macrurus (33), the sides of the suture (h) extend backward 

 toward the scutoscutellar suture (Ic) without meeting. In a great 

 many of the Hymenoptera these separated halves of the scuto- 

 prescutal suture form two distinct longitudinal lines on the anterior 

 notal plate which subdivide the latter into a median and two lateral 

 or parapsidal areas {Euurohracon, 20; Odontaulacus , 22; Erymotylus, 

 33; Syntomaspis, 34; Eurytoma, 46; Tropidopria, 58). The sutures 

 are commonly called the parapsidal sutures, and the entire front plate 

 for convenience may, in such cases, be called the scutum, as it is 

 ordinarily termed. Yet it is evident that the median area (33, 46, 

 Psc^ is the prescutum prolonged posteriorly to meet the scutellum 

 {Scl^, and that the parapsides are the separated halves of the true 

 scutum {Sd^. In some forms, now, these parapsidal sutures (Ji) are 

 absent, as in Tremex (3), Trogus (27), Leucospis (37), Microterys (42), 

 CoccopTiagus (45), Proctotrypes (55), Telenomus (60), Apis (63), and 

 others. In such cases it is to be supposed that the prescutal and 

 scutal plates are fused, and while, for convenience, the anterior 

 plate of the notum may be called the "scutum " it must be remembered 

 that it is really a scuto-prescutal sclerite. In the Hymenoptera the 

 anterior phragma is always attached to the anterior edge of the 

 mesonotum and constitutes a prephragma of the mesothorax (3, 4, 

 10, 16, 30, 31, 37, 43, 52, 55, Aph,). 



3. The concealment of the meso postnotum. and its phragma hy in- 

 vagination within the cavity of the thorax. 



The Tenthredinoidea (Arge, 10; Trichiosoma, 16, 19; Lygsenema- 

 tus, 18; and Bactroceros, 17) possess a distinct postnotum in the 

 mesothorax (PN^), consisting of an exposed transverse plate behind 

 the scutellum (Scl^) connected laterally with the mesothoracic 

 epimera {Epm^). It is visible externally also in Tremex (lyPN^), 

 but is less exposed here than in the Tenthredinoids. In all the other 

 Hymenopteran families, however, is is normally concealed from view 

 beneath the metanotum, for it is entirely invaginated into a pocket 

 between the mesothorax and the metathorax, but when the me- 

 sotergum is removed from the surrounding parts the postnotum 

 (PN^) and its phragma iPph^) are brought to light {Trogus, 30; 

 Alomija, 31; Leucospis, 37; Proctotrypes, 55). Lateral arms of the 

 the postnotum usually maintain a hidden connection with the pos- 



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