40 ORTHORRHAPHA. 



The suborder ORTHORRHAPHA is divided into two groups, the 

 NEMATOCERA and the BRACIITCERA (meaning " thread-horn " and 

 "short-horn" respectively), which are distinguished from one 

 another by the following characters : 



NEMATOCERA, Latr. 



" Palpi pendulous ; generally 4- or 5- jointed, and more or less 

 filiform. When (as in Aedes and some genera of CECIDOMYIDYE) 

 there are only one or two joints, the structure of the antennae 

 and the venation remove all doubts." (Verrall, " British Flies,'' 

 1909.) 



Antennge composed of two basal joints (which are practically 

 always differentiated from the others and known as the scape) 

 and a flagellum of several joints (at least 6, generally 8 to 1C, 

 occasionally as many as nearly 40),* which are homologous, that is 

 to say, closely resembling one another.f They are most usually 

 oval or cylindrical, not infrequently bead-like, sometimes disciform, 

 flask-shaped, pectinate or thread-like. The antennae of the male 

 in many cases (CuLiciME, CHIRONOMIDJE, CTENOPHORINI, etc.) 

 differ very considerably in vestiture from those of the female. 



Wings with a venation varying from a simple form (CECJDO- 

 MTiDjE and some CiiiRONOMiDjE, etc.) to a very complex form 

 (in most TIPULIDJS). Anal cell (when present) wide open,J and 

 with a tendency to greater width at the wing-margin ; as con- 

 trasted with the BRACHYCERA, in which it is, as a rule, closed 

 before the margin of the wing ; or when open, it is nearly always 

 narrowed towards and at the wing-margin. The 2nd longi- 

 tudinal vein often furcate, the 3rd vein rarely. Discal cell 

 rarely present, except in TITULIDJE (in which it is also not infre- 

 quently absent or capricious, according to the individual) and in 

 the KHYPHUXE. 



" In all cases of doubt as to whether a fly belongs to the 

 .NEMATOCERA, through the palpi being onlv one- or two-jointed (as 

 in Aedes or some genera of CECIDOMTID^E), the structure of the 

 antenna? and the venation should remove all doubt. When the 

 antennae are shortened, and the flagellum ( = 3rd joint) is appa- 

 rently only annulated (as in the BIBIONID^E, SIMULIIDJE and 



* Some authors dispute this, sayiug 28 is the highest number known. 



t This term is used here in the same sense as Mr. Verrall employs it in his 

 clasaificatory introduction to the second published volume (vol. v.) of his 

 "British Flies." That is to say, in its popular and ordinary sense of 

 "having the same relative position, proportion, value or structure, and not 

 in its zoological sense, that the hand of a man and the fore-foot of a horse are 

 liomolognes." 



\ The only exceptions occur in a few BIBIONID.E. 



Williston adds, " if ever." I have in the present work temporarily 

 recognised a certain forked vein in some genera of BIBIONID^E as the 3rd and 

 not the 2nd longitudinal, although having doubts on the subject; and this 

 prevents a statement that the 3rd vein is never furcate in the NEMATOCERA. 



