52 



[February, 1903. 



Fig. 5. — Hind-wing of a Cbcesus. 



k f 



k 



Nervures in abore Figure. 

 af, costa ; h f, subcosta ; c v, medius ; d x, brachius ; e g, humerus ; ax, axillus ; 

 h i k, radius ; z n y, cubitus ; I z q, discoidal ; i n, cubital ; m s, medial ; r w, areal. 

 Longitudinal and transverse nervures distinguished as in Fig. 4. 



The most conspicuous difference between the upper and lower wings is the great 

 deyelopment in the latter of the anal field (the portion lying between the humerus 

 and the interior margin of the wing). This is extremely broad, and contains a special 

 nervure of its own called by Konow the axillus (« x). It is not always easy to 

 examine this part of the wing, as it is apt to get creased upwards and folded almost 

 like the wing of a " Diplopteron]" (Wasp). 



The main longitudinal nervures are the same, only the brachius generally reaches 

 the margin, so that the brachial area reaches right across the wing, and is longitu- 

 dinally separated from the anal. 



The transverse nerves are similarly arranged but reduced in number, and the 

 discoidal nerve is shifted further towards the apex of the wing. It strikes not the 

 subcosta, but the cubitus at its commencement, which is in this wing not a point in 

 the subcosta, but one pretty distant from it {z). There is indeed a faint shadowy 

 vestige of the original basal part of the cubitus between z and the subcosta ; but 

 practically this vein, in the lower wing, commences where it is met by the discoidal 

 nerve, viz., at z. 



Having thus cut off the basal end of the cubitus, and as it were disconnected it, 

 the discoidal nerve runs on to the radius and ends there at the point /. As to the 

 remaining transverse nerves it may be generally said that in the lower wing there is 

 (1) no radial, (2) one cubital at most, and often none, (3) one medial {= " recurrent") 

 at most and not rarely none, (4) one areal which may end (at w) either before, at, or, 

 as in Fig. 5, after the apex of the humeral area ; and practically that is the whole 

 of the transverse neuration in it. 



Characters derived from the lower wing are — (1) the presence or absence of 

 the cubital nerve — not very reliable, since it is apt to vary ; (2) the presence or 

 absence of the medial nerve — here irregularities are less common ; (3) the almost 

 complete disappearance in certain Genera, e. g., Pseudoditieura, of the humerus, so 

 that the humeral area is thrown, as it were, into the anal; and (4) a singular phe- 

 nomenon which may be described as follows: — 



