CH. XIV] CLASSIFICATION 259 



production, by convergence, of closely similar, highly reduced 

 types. It is the duty of the systematist to try to separate the 

 converging threads of descent, to give due weight to the imaginal 

 characters still left over, and, by a judicious study of larval forms, 

 to separate those groups in which the imaginal characters fail 

 or are deceptive. The recent separation of Synlestes from the 

 Megapodagrioninae is a case in point [176]. 



The classification here given does not go beyond tribal limits, 

 except in indicating here and there the existence of two or more 

 series within a large tribe. For a list of genera, arranged in their 

 correct zoo-geographical regions, the reader is referred to the 

 tables in the section on Entogenic Fauna in chap, xv, and to 

 the section on Palaeogenic Fauna in the same chapter. 



Order ODONATA. 



Suborder ANISOPTERA. 



Wings held horizontally or depressed in repose (except Cordulephya). 

 Hindwing always more or less considerably broader than forewing near the 

 base. Radius branched, the radial sector crossing two branches of the media. 

 Oblique vein and bridge present. Discoidal cell differentiated into triangle + 

 supertriangle. Eyes large, often meeting mid-dorsally, never separated by 

 a space greater than their own diameter. Labium variable. Male with two 

 superior and one inferior anal appendages, all placed dorsally above anus; 

 the inferior may be bifid or trifid. Penis jointed. Female with superior 

 appendages but no inferior appendage. Ovipositor variable. 



Larva proctobranchiate (i.e. with gills in rectum). Anus closed by an 

 anal pyramid formed of three spines, one medio-dorsal (appendix dorsalis) 

 and two lateral (cerci). Gizzard with four to eight dental folds. 



Family 1. AESCHNIDAE. 



Triangles of fore and hindwings similar or nearly similar in shape, placed 

 equally distad from arculus. Antenodals of first and second series not corre- 

 sponding, except two conspicuously thickened triangular ones (usually the 

 first or second, and one between the fourth and ninth). Hindwing of male 

 angulated (except in the Anax-Series). Auricles nearly always present on 

 seg. 2 in male, sometimes also in female. Labium with well-developed median 

 lobe, not overlapped by lateral lobes ; the latter with movable hook and end- 

 hook. Nearly always a bicolorous body-pattern. 



Larva with abdomen usually somewhat elongated. Mask flat (except in 

 Cordulegastrinae). Gizzard with four to eight fields, radially symmetrical 

 (except Cordulegastrinae). Rectal gills simplex or duplex, but never lamellate. 



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