1893.) 



cell, at a point farther in than its real ending. The inward termina- 

 tions of the postical and axillar nervures are also often concealed 

 through the density of the hair. When that is the case, worn 

 specimens may supply a ready solution of perplexities, or it may 

 suffice to denude the under-surface of the wing in that region, and 

 shift the specimen about in different directions towards the light 

 during its examination. Denudation of wings is easily effected under 

 a lens, while the specimen is on the pin, with the aid of a very narrow 

 strip of kid leather cut to an attenuated point, finishing touches being 

 given afterwards when the wing is detached, and lying upon smooth 

 paper. Fine hedgehog's bristles are useful at this stage. The wing 

 can then be mounted between glass as an object for the microscope, 

 and be placed in the cabinet for future reference. Wings of nearly 

 all the species here described have been thus treated. 



As a standard of reference, the wing of a common species of 

 Pericoma has been selected. 



Wing or Pericoma nubila.. 



Neevuees : — 1, media- 

 stinal ; 2, subcosta ; 

 3, 3', radius ; 4, cubi- 

 tus ; 5, prsebrachial ; 

 6, 6', pobrachial ; 7, 

 postical ; 8, anal ; 9, 

 axillar. 

 Basal cells: — A, an- 

 9 " terior ; B, posterior. 



When more convenient, the 2nd, 3rd, and 4th nervures are desig- 

 nated by adjectives — subcostal, &c. The nervure connecting the end 

 of the inner margin with the extreme wing-roots has no term applied 

 to it ; in Sycoraoc it is disconnected from the margin. 



The homologies attributed to the nervures are open to discussion. 

 Compared with the wing of Epliemera {of. Trans. Linn. Soc. London, 

 ser. 2, Zool., vol. iii, pi. viii, 12a), that of Pericoma appears to lack 

 the sector (unless the branch of the radius 3' be reckoned a sector, as 

 it might well be) ; and in place of two intercalaries between the anal 

 and pobrachial nervures, Pericoma has a single nervure termed the 

 postical. In the next place, on comparing the Analytical Key, given 

 below^ with Haliday's tabulation of the genera (Walk., Ins. Brit. 

 Dipt., iii, 254, step a a), a difference is noticeable in the use of the 

 term cubitus or cubital. Haliday himself is not uniform in his appli- 

 cation of this term : in his description of Psychoda {op. cif., p. 255) 

 it is applied to tie posterior of the two nervures intervening between 



