312 T. J). A. Cockerel! — Descriptions of Tertiary Insects. 



deri • a little more basad in Nemestrina A., and distinctly 

 more apicad in Ilirmoneura clausa. 



(2) Subcosta similar in all the species of Ilirmoneura, but 

 ending somwhat further from the apex in II mdcanica (nearly 

 3 mm from tip of wing) and II clausa ; ending still further from 

 apex in Nemestrina A. 



(3) Radius (E.) is practically the same in ail. In H. vulcan- 

 ica it and the subcosta are very thick veins, contrasting with 

 the other longitudinal veins, all of which are slender. 



(4) Radial sector, or R 2+3 . Practically the same in all. In 

 U. vulcanica it rises rapidly at the cross-vein, as shown in 

 the figure. 



(5) Radial cell. In all very long ; the cross-nervure, which 

 in many Diptera is very short, having become greatly elon- 

 gated, and also very oblique, so that it forms more than half of 

 the upper side of the cell. In Nemestrina A. and Ilirmoneura 

 B., as also in Proliirmoneura, the cell terminates at the point 

 of origin of the second mediocubital cross-nervure; but in 

 H. melanderi it falls a little short of this, and in II. mdcanica 

 and clausa the distance is considerable. This is shown in the 

 accompanying figures, where the little fork on the right side 

 of the diagram is the end of the radial cell. 



(6) Third radio-medial cross-nervure. This nervure is absent 

 or not preserved in Proliirmoneura. In H. melanderi it is 

 very long, and looks like a branch of the radial sector. In the 

 others it is oblique but much shorter, as is shown in the figures 

 (the nervure connecting R s with M). 



(T) Media. In Proliirmoneura it simply forks ; in Nemes- 

 trina A. it forks, but the branches are bulged outwards at the 

 base ; in Hirmoneura B. the upper branch has been deflected 

 basally by the cross-nervure, so that there is a small false cross- 

 nervure at the bifurcation ; in the other species the false cross- 

 nervure is large, as the figures show. In H. clausa the 

 branches of the media meet again, enclosing a cell. 



(S) Cubitus. The branching differs in its relation to the 

 first cross-vein, as the figures clearly indicate, a verbal descrip- 

 tion being unnecessary. It is remarkable that in this, as well 

 as in some features of the media, the recent species, especially 

 Ilirmoneura B. and Nemestrina A., are nearer to the Prohir- 

 moneura condition than are the Florissant fossils. The apical 

 cell between the branches of the cubitus is open in all except 

 H. clausa. 



(9) Cubital cell is just closed in II. clausa ; in the others, 

 narrowly open. According to my interpretation, the vein 

 bounding it apically is a cross-nervure, and not a branch of the 

 cubitus. If this is correct, the vein which Comstock and ISTeed- 

 ham call Cu 2 in Testis, Dixa, etc., is apparently this same cross- 

 nervure, and their M„ and Ciij are Cu, and Cu 2 . 



University of Colorado, Boulder, Colo., November 11, 1907. 



