10 INTRODUCTION. 



longitudinal vein * between its origin and the point of forking is 

 called the pnefarca ; the two branches, after forking, are the 

 "anterior and posterior," the "upper and lower,'"' or the " fore 

 (or front) and hind," respectively.t 



It may be noted here that Mr. Verrall uses the terra prrcfurca 

 for the " common origin " of the 2nd and 3rd longitudinal veins, 

 that is to say it terminates at the origin of the 3rd vein, but it is 

 adopted in the present work in Osten Sacken's sense, comprising 

 tlie whole of the 2nd vein as far as the fork. The section of the 

 praefurca between the origin of the 3rd vein and the fork of the 

 2nd is often referred to as the petiole of the 1st suhmavginal cell. 

 IS^aturally this only applies \Ahen the 2nd vein is forked, as 

 otherwise there is only one submarginal cell. 



The marginal cross-vein is placed near the tip of the 1 st longi- 

 tudinal veil), joining it to the 2nd vein and dividing the 

 marginal cell into two parts, often into about equal halves, these 

 being known as the inner and outer marginal cell respectively. 

 When the 2nd vein is forked this cross-vein may unite with the 

 upper branch or with the prasfurca, and it has a tendency to 

 indistinctness in many species. It is present in the large majority 

 of genera ia Tipulid^e, but is absent iu some (Atarha, Toxorliina, 

 RhampJiidia, etc.) ; it is indistinct in Limnoj^liUa, present in 

 Ptijclioptera and the Tipulin.^, whilst in the Ctlindkotomini it is 

 replaced by a small and often indistinct cross-vein between the 

 Ist longitudinal vein and the costa. The value of its presence or 

 absence has been over-estimated by one or two authors, although 

 it can usually be accepted as a good character. 



l"'he 3rfZ longitudinal vein emerges from the pr?efurca in nearly 

 all the TiPULiD.^, J and the praefurca itself is often bent do\\nwards 

 at a more or less distinct angle at the point of contact. The 3rd 

 vein is simple in all the Oriental genera, except in the subfamily 

 Ptychopterin^, iu which its forked nature constitutes one of 

 the principal characteristics of the group. It is nearly always 

 present, any genus without it being most abnormal. In Toxo- 

 rhina it is altogether absent, the anterior cross-vein connecting 

 the 2nd and 4th longitudinal veins ; in Mongoma (according to 

 my interpretation of the venation) it is reduced to a short longi- 

 tudinal connecting vein between the middle of the praefurca and 

 the 4th longitudinal, thus not even approaching the margin of 



* It will be understood that the abbreviation " Ist Teiu," " 2nd vein,'' " 3rd 

 longitudinal," and so on, in all instances means the 1st longitudinal rein, 2nd 

 longitudinal vein, 3rd longitudinal vein, etc. 



t When once the principle is tlioroughly understood that it is tlie second 

 longitudinal vein vrhicb forks in Tipulid.e (and hardly ever the fhird), it is 

 not of great consequence what may be the exact terms used ; nor is there any 

 unanimity in the matter. In company with other authors I use all the 

 terms quoted indiscriminately. 



I The principal excejition is Amalopis, in which it emerges either from the 

 posterior branch of the 2nd vein or from the praefurca, according to the 

 species. 



