602 ON THE GENUS DIPHLEBIA, 



median nei'vures in the wing of J). ni//>ipho'ides cf is a strong 

 proof of specialisation being successful in this genus. Who 

 knows but that, in some far remote past age, an ancestor of 

 the whole of the present Odniiafa brought about the fusing 

 of the radius and median nervures in the same manner ! One 

 may wonder even that a petiolat-; wing with only four main 

 basal nervures, subcubitus + radius + median forming an exceed- 

 ingly strong second nervure, has not taken its place amongst the 

 more highly specialised and successful zygopterous types of the 

 present daj'. 



Revision of the Genei^ie Definition . 



The characters of the genus, as defined by de Selys, need 

 some slight modification, in order to include the four closely 

 allied species now known. De Selys states, for instance, that 

 in Dijihlehifi, there are sectors interposed between M4 and 

 Cu,. I find this to be the case only in a few of my specimens 

 of D. lestoules, and then usually in the hind-wing. The 

 divergence of M^ and Cu^ towards the margin of the wing 

 results in an increase of the number of cell-rows from one to 

 two, and finally to three or four at the wing-margin (Plate 

 XX., fig. 1), but the borders of the rows are not usually 

 straightened out into a true sector, but remain in the less 

 specialised condition shewn in the figure. This generic charac- 

 ter, therefore, needs revision. Another point is the position 

 of departure of M„ from Mj. In most of my series, of all 

 four species, M^ continues in an almost unbroken curve from 

 the nodus itself, though in some specimens there is a distinct, 

 but not very sharp, break at the join. A third point is that 

 de Selys describes the male superior appendages as "semi-cir- 

 culaires, simples." This coiild hardly include the peculiarly 

 shaped appendages of D. hi/hrido'/des with their large inferior 

 spine. Again, de Selys says that the nodus in Dijihlehia is 

 placed a little less than one-half the wing-distance from the 

 base of the wing. Taking D. niimjilio'irles, the nodus is onlv 



