436 PROCEEDINGS OF THE NATIONAL MUSEUM vol. no 



including those of Ichneumonidae and Braconidae, and many para- 

 sitize the egg cocoons of spiders. 



Phygadeuon, helix, StUpnus, and Atractodes resemble each other in 

 larval characters and all are parasites of muscoid Diptera. Dis- 

 tinctive features of Atractodes are that the head and the base of the 

 mandibles are lightly sclerotized and the well-sclerotized blade of the 

 mandible is toothless, the several very small ridges present on the 

 dorsal surface of the blade not being distinct enough to be called teeth. 

 The antenna, like that of Stilpnus, is disc-shaped, but StUpnus differs 

 from Atractodes not only in the key characters but also in having the 

 blade of the mandible more slender, the ventral part of the labial 

 sclerite more sharply narrowed in the median line, and the posterior 

 end of the hypostoma straight instead of slightly bent towards the dor- 

 sal surface (compare figs. 19 and 64). 



The following are figured in the literatm-e: Otacustes crassus 

 patruelis (Cushman) (Clancy, 1946), Gelis melanoceyhala (Schrank) 

 (Beu-ne, 1941), G. tenellus (Say) (Clancy, 1946), Hemiteles areator 

 (Panzer) (Morris, Cameron, and Jepson, 1937), H. hemipterus (Fab- 

 ricius) (Salt, 1931), H. simillimus (Taschenberg) (Blunk, 1952). 



Tribe Aptesini 



Figures 20-21a 



Most of the members of this tribe are parasites of sawflies. Char- 

 acteristics of the larvae are the development of the lateral parts of the 

 epistoma dorsal to the anterior tentorial pits and the relatively large 

 mandibles. The teeth on the dorsal surface of the blade of the mandi- 

 ble are larger than the teeth on the ventral surface in Aptesis and 

 Rhemhohius but not in Cubocephalus. 



Larval Key 



1. Teeth on the dorsal surface of the blade of the mandible not markedly larger 



than teeth on the ventral surface Cubocephalus 



Teeth on dorsal surface of blade of mandible larger than teeth on ventral 

 surface 2 



2. Blade of mandible short, broad, and well-sclerotized, with length approximately 



equal to one-third of that of base of mandible Rhembobius 



Blade of mandible relatively slender with length approximately equal to one- 

 half of that of base of mandible Aptesis 



The following have been examined: Cubocephalus sp. (fig. 20a), 

 Aptesis indistincta (Provancher) (fig. 20b), A. pteronorum (Graven- 

 horst), and Rhemhohius abdominalis (Provancher) (fig. 21a). 



The teeth on the dorsal surface of the blade of the mandible of A. 

 pteronorum are smaller than in A. indistincta. 



