SUBPHYLUM III 



INSECTA 



811 



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

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

 wings. Half a dozen species are known from the Ujiper Jura, and a considerably 

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

 Miocene of Europe and North America. Dysac/rion Scudder is represented by a few 

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



Fio. 1569. 



Cymatophlebia longialata (Germar), 

 Litliographic Stone ; SolbAhofen, 

 Bavaria, '^fi. 



Fio. 1570. 



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

 Colorado. 3/j. 



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

 Here also occurs Argia aliena (Scud.) (Fig. 1570), together with representatives of 

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

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

 Cockerel!, which has been made the subject of special investigation by P. P. Calvert 

 {Proc. Acad. Nat. Sci. Philacl, May 1913). 



Order 28. MEGALOPTERA 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 being moderately numerous, 

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

 homonomous, loith five -jointed tarsi; cerci usually 

 reduced, ovipositor not prominent. Larvae of acpiatic 

 habits, 2}ossessed of branchiae and legs, but no spiracles, 

 and with mandibles formed for biting, armed ivith strong 

 teeth. 



Fio. 1571. 



This group has a long geological history, extending f,,^^^,;^^^,, ^,;,„, pjetet. Lower 

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

 proljably descended from Palaeodictyopteroid ancestors. ^^'^^'^ '' 



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

 (Bunter) of Germany, and an undoubted larval form, Mormolucoides articulatus 

 Hitchcock, is not uncommon in the Upper Trias of Turner's Falls, ]\Lassachusetts. 

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



