10 INTRODUCTION. 



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

 called the prcefurca -, the two branches, after forking, are the 

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

 (or front) and hind," respective! y.t 



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

 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 

 the 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 submarginal cell. 

 Naturally this only applies when 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 vein, 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 pra^furca, and it has a tendency to 

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

 of genera in TIPULID^:, but is absent in some (Atarba, Toxorltina, 

 Rhamphidia, etc.) ; it is indistinct in Limnopldla, present in 

 Ptychoptem and the TIPPLING, whilst in the CYLINDEOTOMINI it is 

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

 1st 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. 



The 3rd longitudinal vein emerges from the praefurca in nearly 

 all the TIPULID^E, J and the prsefurca itself is often bent downwards 

 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 

 PTYCHOPTEBIK^E, in 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 praafurca and 

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



* It will be understood that the abbreviation " 1st vein," " 2nd vein,'' "3rd 

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

 longitudinal vein, 3rd longitudinal vein, etc. 



t When once the principle is thoroughly understood that it is the second 

 longitudinal vein which forks in TIPCLID.K (and hardly ever the third), 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. 



J The principal exception is Amalopis, in which it emerges either from the 

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

 species. 



