252 PROCEEDINGS OF THE ACADEMY OF [May, 



origin of Ms (see Table I), have but one such cross-vein. Tarsophlehia 

 eximia had five in its hind wing (these veins are not preserved in the 

 front wing) and Steleopteron had two. 



16. The Obliquity of the Quadrilateral. — The shape of the quadri- 

 lateral becomes more oblique with the greater divergence of its 

 proximal and distal sides. Prof. Neeclham has assumed" that a 

 nearly rectangular quadrilateral, in which opposite sides are parallel 

 to each other, is the more primitive form and that from it at least 

 two kinds of oblique quadrilaterals have arisen. There seems to be 

 no published ontogenetic evidence in favor of this view and the only 

 paleontological evidence not contradicting it is limited to that 

 puzzling Liassic form, Protomyrmeleon, in which, if Handlirsch's 

 interpretation of the venation be correct,^^ R and M are still distinct 

 from the base distad, and there is no trace of a beginning arculus. 



On the other hand, all the Jurassic fossils, which are not clearly 

 Anisoptera, show an oblique quadrilateral with its posterior distal 

 angle acute.'^* This holds true not only for those fossils referred by 

 Handlirsch to the Zj^goptera like Euphceopsis and Steleopteron, or 

 for forms regarded by him as ancestral to Zygoptera, as Tarsophlebia 

 (and including a Liassic fragment, T. westwoodi^) , but also for other 

 Anisozygoptera not apparently forefathers of the Zygoptera, as 

 Stenophlebia, Isophlebia, and Anisophlebia . Dysagrion of the Eocene 

 had an oblique quadrilateral, and in fact not one of the published 

 descriptions and figures of Tertiary Zygoptera listed byHandlirsch^^ 

 shows a rectangular quadrilateral; all havje it oblique. 



It therefore seems necessary to regard the oblique quadrilateral 

 as the more primitive and the rectangular as a later appearance. 



''' Genealogic Study, p. 717, fig. 11, p. 731. See also Williamson, 1913, p. 2.59, 

 and figs. 1 and 2 on p. 260. 



'sFoss. /«s., Taf. XLII, fig. 14. 



'^L.c, Taf. XLVII. Hagen, indeed (Paleontographica, X, Taf. VIII, f. 8), 

 shows the quadrilateral of the Jurassic Euphcea longiventris as rectangular. In 

 his description, p. 128, he says, "Noch undeutlicher ist der tibrige Theil des 

 Geaders .... das Viereck ist gleichfalls undeutlich," and he gives no details 

 of its shape. Meunier's photographic reproductions (Arch. Mus. Teyler, 2, VI, 

 pi. XXVI, figs. 81, 82, cf. p. 127), not of Hagen's tj-pe, but of other specimens in 

 the Munich Museum, show the shape of the quadrilateral as indecipherable. 

 Handlirsch (Fossil Ins., p. 580) places Euphcea longiventris Hagen as a synonym 

 of Tarsophlehia eximia Hagen and remarks, "Bezuglich Hagens Euphtea longi- 

 nentris [longiventris] habe ich zu bemerken, dass der von ihm 1. 13 f. 8 abgebildete 

 Flugel allerdings von jenem der Tarsophlebien wesentlich abweicht. Aus der 

 Beschreibung ergibt sich jedoch, dass die basale Partie des Flugels an dem 

 Fossile kaum zu entziffern ist, so dass wir diese Reconstrucktion als werthlos 

 betrachten konnen." 



8» Pass. Ins., Taf. XLII, fig. 6. 



81 L.c, pp. 896-899, 1357. 



