14 ECTBODUCTION'. 



submarginal cells respectively.* Care must be taken in those 

 genera ( Gonom-yia, Mongoma, etc.) in which the fork of the 2nd 

 longitudinal vein is short and nearly perpendicular, giving it the 

 appearance of a cross-vein, for which it might easily be mistaken. 



When the marginal cell is divided by the marginal cross-vein, 

 as is the case with most genera of TIPTJLID^;, the divisions of the 

 cell are known as the inner and outer marginal cells respectively, 

 but when speaking of the united cells the term " marginal cell " 

 is correct. 



It will thus be seen that the 3rd vein has in front of it the 

 submargiual cell, if the 2nd longitudinal vein be simple, and the 

 2nd submarginal cell, if the 2nd vein be forked. 



Immediately below the 3rd vein is the anterior cross-vein, the 

 key to the whole venation. This vein always joins the 3rd and 

 4th longitudinal veins, exceptions being very rare (Amalopis), 

 and it always meets the 4th vein at the discal cell (usually at 

 the anterior upper corner of the latter), when this cell is present.f 

 However, whether the discal cell be present or not, the anterior 

 cross-vein meets the 4th vein exactly or very nearly at the same 

 place. Thus the discal cell in the vast majority of TIPULID.S has 

 the Is* posterior cell in front of it, and (except in TIPULIN^E) the 

 ultimate posterior cell (4th or 5th, etc., as may be) behind it.J 



The anterior cross-vein always bounds on its inner side the 

 1st basal cell, below (or posterior to) which latter is the 2nd basal 

 cell, of varying relative length but always conspicuously longer in 

 TIPULIM; than in most families of Diptera. 



Behind, or posterior to, the 1st posterior cell the other posterior 

 cells run on in numerical order, four being the usual number in 

 this family, less frequently five (Limnophila, Cladura, some 

 Eriocerd] ; occasionally only three (Bittacomorpha, a non-Oriental 

 genus), the last posterior cell being that one of which the posterior 

 cross-vein forms the base. 



Posterior to the 5th longitudinal vein is the anal cell, open in 



* In the case of Piychoptera, where the unusual event of the 3rd longi- 

 tudinal vein forking instead of the 2nd is found, the same rule as to the 

 nomenclature of the cells holds good ; thus the 1st submarginal cell is bounded 

 by the 2nd vein and the upper branch of the 3rd vein, whilst the 2nd sub- 

 marginal cell is bounded by both the branches of the 3rd vein. One or two 

 authors have contended that it would be more correct, when the 2nd vein is 

 forked and the 3rd vein simple, to regard the cells as two marginal and one 

 submarginal ; and when the 2nd vein is simple and the 3rd forked, as one 

 marginal and two submarginal ; that is to say, all cells bounded posteriorly 

 by the 2nd vein would be called marginal cells, and those bounded posteriorly by 

 the 3rd vein, submarginal cells, in each case irrespective of their number. In 

 the conceivable case of both 2nd and 3rd veins being forked, there would be 

 two marginal and two submarginal cells. 



t The only exception inTiPULiD^E amongst Oriental genera is Conotia, Wied., 

 in which the anterior cross- vein is placed very distinctly beyond the discal cell. 



I Of course, when the posterior cross-vein is placed so far distally as to be 

 beyond the limits of the discal cell, the latter is bounded posteriorly by the 

 2nd basal cell. It invariably has the 1st basal cell on its inner side. In 

 the TIPULIN.IE the penultimate, not the ultimate, posterior cell bounds the 

 discal cell posteriorly, on account of the lower branch of the 4th longitudinal 

 vein forking just at the lower basal corner of the discal cell. 



