168 PHILIP p. CALVERT. 



2. The wings of the fossil Goraphine genus Stenophlebia, as they are tigurerl by 

 Hagen (Paleoutographica, X, taf xiii, figs. 4, 5, 6; XV, taf xi, fig. 2, taf xiii, 

 fig. 1) strongly favor such a homology. 



The "upper branch of the subniedian vein" perhaps arose as a quadrilateral 

 cross-vein which became niore and more oblique until it formed the upper side 

 of the triangle, while at the same time the apical (outer) side of the quadrilateral 

 increased in length, carrying the submedian vein and its prolongation, the upper 

 sector of the triangle, farther and farther downwards towards the post-costa and 

 its continuation, the lower sector of the triangle. 



The wings are not perfectly flat, but are folded longitudinally* in 

 such a way that the chief veins lie either on the crest of ridges, or 

 at the bottom of valleys (convex and concave veins of Adolph). Look- 

 ing upon i\\Q upper surface of the wings, the costa, median vein, sub- 

 nodal sector, lower sector of the arculus (short sector) post-costal 

 vein and lower sector of the triangle are convex veins, while the 

 subcostal vein, upper sector of arculus, principal, median and nodal 

 sectors, submedian vein and upper sector of the triangle are concave 

 veins. As Lendenfeld pointed out, this folding of the wings pre- 

 vents their being bent in a direction at right angles to their surface 

 and a consequent loss of effectiveness as the wings strike the air. 



Two characteristic features of Odonate wings are the pterostigraa 

 and the raembranule. The pterostigma is an opaque, colored area 

 between the costa and the median vein near the apex of the wing. 

 It fills usually one cell (true pterostigma) or sometimes several cells 

 (false pterostigma). It is occasionally absent (some Zygoptera), and 

 in one instance present, but not touching the costa (Anomnlagrion). 



The membranule is an opaque area at the anal margin, lying outside 

 the veined portion of the wing, absent or rudimentary in the Zygop- 

 tera, of variable size in the Anisoptera. 



Of the numerous cross-veins to be found in the wings of the 

 Odonata special names have been applied as follows: antecubitals 

 (antenodals Kirby) are cross-veins between the costa and median 

 vein, and the base and the nodus, and of which there are two series 

 — those between co«ta and subcostal, and those between subcostal 

 and median veins; those of the first series may or may not coincide 

 in position with those of the second. 



Note. — The term antenodal or discoidnl cells has also been applied by deSelys 

 and is used here (see Enallagma in the Catalogue, post) to denote those cells in 

 the Agrioninse situated between the short sector and the first sector of the tri- 

 angle, and the outer side of the qiladri lateral and the cross-vein which descends 

 from the nodus. They are, therefore, the homologues of the post-triangular 

 cells of the Anisoptera, but this distinctive name is convenient. 



* This folding is but slight, and does not admit of the wing being closed upon 

 itself, as in the Orthoptera, for instance. 



