SUBPHYLÜM III 



INSECTA 



811 



In tlie suborder Zygoptera tlie wings are eqiial, no triangle is formed by the 

 cubitus and cross-veins, and tlie nodal region is situated very near tlie base of the 

 wings. Half a dozen species are known from tlie Upper Jura, and a considerably 

 larger number, mostly belonging to the faiiüly Agrionidae, occur in the Oligocene and 

 Miocene of Europe and North America. Dysagrion Scndder is represented by a few 

 species in the Green River Eocene of Wyoming, and several species closely related 



Fig. 1569. 



Cymaiophlebia longialata (Germar), 

 Lithographie Stone ; yolenhofen, 

 Bavaria. ^/s- 



Argia aliena (Scudder). Miocene lake beds ; Florissant, 

 Colorado, '^/i- 



to living forms are known from the Miocene lake beds of Florissant, Colorado. 

 Here also occurs Ärgia aliena (Send.) (Fig. 1570), together with representatives of 

 several related forms, such as Melanagrion Cock. ; Lithagrion Send. ; and Hesperagrion 

 Calvert. The most interesting dragon-fly from this locality, however, is Phenacolestes 

 Cockerell, which has been raade the subject of special investigation by R P. Calvert 

 {Proc. Acad. Nat. Sei. Philad., May 1913). 



Order 28. MEGALOPTBRA Latreille. (Alder-flies). 



Head with prognathous orthopteroid mouth parts and multiarticulate antennae. 

 Four membranous wings of moderate size, meeting in repose over the hack at an 

 angle ; the hinder pair slightly the smaller ; anal area plicate. Venation of a some- 

 what archaic type, the nervures and transverse veinlets heing moderately numerous, 

 and forming irregularly disposed cells. Segments of the thorax nearly equal, legs 

 homo7iomous, with five - jointed tarsi ; cerci usually 

 reduced, ovipositor not prominent. Larvae of aquatic 

 hahits, possessed of hranchiae and legs, hut no spiracles, 

 and with mandibles formed for hiting, armed with strong 

 teeth. 



Fi(». 1Ö71. 



This group has a long geological history, extending (,^„„^.,^,, j^^^m Pictet. Lower 

 from the Jjower Trias onward to the present day, and is oligocene ; Baltic amber. ■*/.! (after 

 probably descended from Palaeodictyopteroid ancestors. ^^^^^^)- 



The genera Ghauliodites Heer, and Triadosialis Handlirsch occur in the Lower Trias 

 (Bunter) of Germauy, and an undoubted larval form, Mormolucoides articulatiis 

 Hitchcock, is not uncommon in the Upper Trias of Turner's Falls, Massachusetts. 

 In this latter a head, or thorax, of tliree segments, and an abdomen of nine segmeiits 



