40 ORXIIORRIIAPHA. 



The suborder Orthorrhapha is divided into two groups, the 

 Nematocera and the BuACiiroERA (meaning " thread-horn " and 

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

 another by the following characters : — 



JS^EMATOCERA, Latr. 



" Palpi j)e7iduloi(s ; generally 4- or 5- jointed, and more or less 

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

 there are only one or two joints, the stru.cture of the antennse 

 and the venation remove all doubts." (Yerrall, " British Elies," 

 1909.) 



Antennte composed of two basal joints (which are practically 

 always differentiated from the others and known as the scape^ 

 and a Jiagellum of several joints (at least 6, geniirally 8 to 16, 

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

 to say, closely resembhng one another.t They are most usually 

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

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

 in many cases (Culicid.e, Chironomid^, Ctexophorixi, etc.) 

 differ veiT considerably in vestiture from those of the female. 



Wings with a venation varying from a siuiple form (Cecido- 

 MYiD^ and some Cuironomid.e, etc.) to a very complex form 

 (in most Tipulid^e), Anal cell (when present) wide open,^ and 

 with a tendency to greater width at tlie 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 

 iiarro«ed towards and at tlie wing-margin. The 2nd longi- 

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

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

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

 the Rhypiiii)^. 



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

 A'ematocera, through the palpi being only one- or two-jointed (as 

 in Aedes or some genera of Cecidomyid.e), the structure of the 

 anteinite and the venation sh(»uld remove all doubt. When the 

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

 rently only annulated (as in the Bibionid^, SiMULiiDyE and 



* Some aiitliors dispute tliis, sayiug 28 is the bigliest number known. 



t This term is used here in tlio same sense as Mr. Verrall employs it in Jiis 

 class] ficatory introduction to tlie 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 zooloffical sense, that the band of a man and the fore-foot of a horse are 

 homologues." 



I The only exceptions occur in a few BiBioNin.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 Ne.matocera. 



