4 DIPTERA OF NORTH AMERICA. [PART IV. 



aud Ilaliday places it provisionally, togetlier with Orplinejihila, 

 in an artificial group, Heteroclitae. Dixa has no thoracic suture ; 

 the ovipositor of the female, according to Mr. Halidaj, is different 

 from that of the Tipulidse, consisting of two short, broad, round 

 lamels ; the presence of only six longitudinal veins, the shortness 

 of the auxiliary vein, the absence of both subcostal and marginal 

 cross-veins, the peculiar course of the first longitudinal vein, the 

 constant absence of the discal cell, etc., constitute a type of 

 venation which separates Dixa from all the known Tijndidse and 

 shows some points of analogy with Ptychoptera only. The 

 rather extraordinary larva of Dixa (described by Stseger) is one 

 ground more for separating this genus from the Tijnclidse. Alto- 

 gether, I incline to the opinion of Mr. Haliday in leaving Dixa, 

 temporarily at least, in an isolated position. 



« 

 2. On the larvae of the Tipulidse. 



During the larva stage, the species of this family are as well 

 marked among the Diptera, as in the perfect stage of their 

 existence. At the same time, they exhibit a remarkable con- 

 forraity in the more important parts of their organization, all the 

 differences in the external conditions of their life notwithstanding. 

 About a dozen more or less complete descriptions of such larvfe 

 have been given by former authors,^ and I have had occasion 

 myself to examine several larvae of Limnohia, Tipida, Pachyr- 

 rhina, and Ctenophora. The following account is based upon 

 these data (some more details concerning all the known larvae 

 of this family will be given under the head of the respective 

 genera) : — 



The principal character, distinguishing these larvce from those 



' Ferris, Anti. Soc. Entom. de Ft. 1849, p. 331, Tab. VII, f. 4 {Ula 

 pilosd) ; the same, 1. c. 1847, p. 37, Tab. I, f. 3 (Trichocera) ; the same, 

 1. c. 1849, p. 331, Tab. VII, f. 5 (Limnophila dlspar) ; Chionea by Brauer 

 ( Verh. Zool. Bot. Ver. 1854) ; Cylindrotoma in Schellenberg, Genres de 

 Monches Dipt., aud in Zeller, Ms, 1842, p. 808 ; Phulaci-ocera in Degeer; 

 Ptychoptera in Reaumur and Lyonnet ; Ctenophora in Fischer, Ori/clogr. 

 du Gouvt. de Moscou, Bouche, etc. ; Tipula in Eeaumur, Degeer, Bouche, 

 etc. Besides the detailed descriptions, numerous short notices about 

 single larvse are scattered in the different authors. I cannot refrain from 

 noticing here, that what Mr. Heeger describes as the larva of Limnohia 

 plati/ptera Macq. (Sitzungsber. der Wien. Acad. Vol. XI, 1853) is a Myceto- 

 philideous larva, probably Bolitophila. 



