CH. XVTIIj BRITISH SPECIES 339 



should be made for possible changes in details. The females of 

 Agrion are very difficult to separate. The best rule is always 

 to try and capture males from the same spot ; if possible, in coitu. 

 Where two or more species of Agrion occur together (as on the 

 Norfolk Broads) pairs in coitu should be taken. The student may 

 then study them carefully until he is familiar with their facies. 

 A reliable key can be constructed from a comparative study of 

 the outlines of the prothorax in both sexes. 



The classification of the larvae is a difficult matter, partly 

 owing to the great similarity of the larvae in some genera (e.g. 

 Sympetrum, where even the expert is at a loss to find specific 

 differences) and partly because many species are still not known 

 for certain in their larval forms. The student is referred to figures 

 of larval forms typical of the different genera. Having mastered 

 these, he may then use the short descriptions given, which sum- 

 marize the principal differences for the known larvae. 



(N.B. All measurements are given in millimetres.) 



Suborder ANISOPTERA (Characters, p. 259). 



Family AESCHNIDAE (Characters, p. 259). 



Subfamily Gomphinae (Characters, p. 260). 



Tribe Gomphini (Characters, p. 261). 



Genus I. Gomphus Leach (fig. 118). Coloration black and yellow; thorax 

 with dorsal, ante-humeral and humeral black bands. 



1. G. milgatissimus Linn. abd 32 34, hw 29 31., pt 2-5, dark brown. 

 C black. Occiput straight, yellow, with black hairs. Abd. with a mid-dorsal 

 yellow line on 1 7 ; 8 9 considerably dilated. App. sup. short, black, 

 suddenly pointed; inf. with divergent cornute branches. ? abd 34 35, 

 hw 31 32, pt 3. Stouter; abd. thicker, more cylindrical; yellow markings 

 in general more evident. Very rare. June. 



Subfamily Cordulegastrinae (Characters, p. 262). 



Genus II. Cordulegaster Leach (fig. 121). Robust Aeschna-like species. 

 Coloration black and yellow ; $ with hard black ovipositor reaching beyond 

 end of 10 (fig. 101). 



2. C. annulatus Latreille. Q <*-bd 55 58, hw 41 48, pt 4, black; memb. 

 whitish ; C yellowish in front. Thorax with three pairs of wide and one pair 

 of narrow yellow bands. Abd. black with median narrow yellow bands 



222 



