INTRODUCTION. n 



nervuves, one between the ■postcostal and the mrdlan, and 

 the other between the m'dum and jposterior nervures, are 

 called the upper and lower basal cells. These cells exist 

 in nearly all our British genera. From this transverse or 

 basal nervure, as it crosses the upper basal cell, extends 

 a nervure towards, but rarely attaining to, the apical margin 

 of the wing. This, which is called the cubital nervure, is 

 united by one or more transverse nervures to the ])Osterior 

 nervure of the marginal cell, enclosing thereby one, two, 

 or three cells called the sub-marginal cells. 



The cubital nervure emits posteriorly two others called 

 the recurrent vervures. The basal one of these unites 

 it with the median, forming the first discoidal cell. A 

 nervure running from this point of union to the posterior 

 nervure creates another cell, called the second discoidal. 

 From the centre of this cell's outer nervure, a longitudinal 

 nervure is emitted, which meets the second recurrent, thus 

 forming a cell called the ilvird discoidal. From the extero 

 posterior angle of this cell a nervure sometimes extends to 

 the apical margin of the wing. When this is so two more 

 cells are formed, called the first and second apical cells ; 

 some of these cells, especially those on the posterior apical 

 portion of the wing, are frequently wanting. 



In the posterior wings there are three main longitudinal 

 nervures — the anterior, which runs nearest to the anterior 

 margin, the median and the posterior. The anterior is some- 

 times united to the actual anterior margin of the wing near 

 its centre, and is nearly always united by a cross vein to the 

 median, which again is usually united by a cross vein or 

 a curved nervure to the p)osierior. On the front margin of 

 the posterior wing is a series of fine hooks, by which the 

 wing can be hung on to the anterior one. The wings are 

 nearly always hyaline, but occasionally dusky, and in 

 Fsitliyrus rupestris $ nearly black. 



The legs are each composed, as in other insects, of coxa, 

 which is usually large and swollen ; trochanter, which is, 

 nearly always single, but in a few genera of the Fossores 



