292 



other tribe, but Bibionoidea should constitute a new tribe and 

 Cecidomyioidea remain as the only superfamily in Oligoneura. 



CHARACTERS OF THE TRIBE 



Larva. — In some respects the larvae of Cecidomyioidea are very 

 primitive; in fact, if we consider their respiratory system — which is 

 almost without exception functionally peripneustic — and the number 

 of segments (13) as of primary importance we must place these in- 

 sects with the most generalized of the Diptera. But, probably owing 

 to the mode of life of the larvae, the head has undergone considerable 

 transformation, until, with the absence or vestigial nature of the man- 

 dibles and the almost invariable reduction of the head-capsule poste- 

 riorly, we have what is undoubtedly a much specialized form. The 

 much reduced heads of these larvae separate them readily from other 

 Nematocera. 



The Bibionoidea differ from the foregoing in having the head-cap- 

 sule complete and the mandibles developed ; and in that all the species 

 known in the larval stage have lateral abdominal spiracles — some 

 functional and others not. The species of Bibio known to me have 

 apparently 13 segments in addition to the head, and 8 pairs of lateral 

 spiracles in addition to the prothoracic and anal pairs — characters 

 which indicate that they are very primitive. The aquatic forms 

 (Simuliidae) have peculiarly modified mouth-parts, and because of 

 their living in running water show adaptations in other respects. The 

 Bibionidae and Scatopsidae are terrestrial, and while the lateral ab- 

 dominal spiracles are present, I believe that in some cases they are 

 doubtfully functional. 



Pupa. — The pupae of both superfamilies are structurally primi- 

 tive. The head in the species of Cecidomyiidae that live in galls is 

 armed with sharp chitinized thorns b)^ means of which the pupa bores 

 its way to the surface prior to the emergence of the imago. The other 

 members of the tribe possess no cephalic thorns. The thoracic re- 

 spiratory organs are sessile in most species, being elongated only in 

 Scatopsidae, Simuliidae, and a few Cecidomyiidae. For other charac- 

 ters see synoptic keys and descriptions of families. 



Imago. — See synoptic key to the imagines of Nematocera. 



Superfamily Cecidomyioidea 



But one family is referable to this superfamily. It is of consider- 

 able extent, world-wide distribution, and of much economic impor- 

 tance. 



