INDIAN DRAGONFLIES. 155 



Orthetrum, Newman (1833). 



Libelia, Brauer. 



Hydronyitiplia, Buchecker. 



Head moderately large ; eyes shortly or rather broadly contiguous; fore- 

 head prominent, with a distinct foreborder, flattened, above and in front, 

 the flattened zone very glossy, the borders rounded and the shape in both 

 sexes nearly similar; sutures moderately flush; vesicle variable, either 

 nearly rounded or somewhat notched above. 



Prothorax . lobe large, projecting, fringed with a rufi:' of long hairs, 

 generally notched in tbe middle. 



Thorax robust. 



Legs moderately long, very robust. Hind femorse with a row of closely- 

 set, numerous, moderately even, short spines and at the distal end, 2 or 3 

 somewhat lunger ones ; mid-femorse with fewer, gradually lengthening 

 spines ; armature of the feniorse of the female similar to that of the mid- 

 femorjje of the male; tibial spines not numtrous, 8 to 12 in number, stout, 

 distant, upright or somewhat sloping; claw-hooks close to base of claws, 

 robust. 



Wings long, the hind moderately broader than the fore ; the trigone of 

 the forewing in line with that of the hiud ; arc usually at the 2ud antenodal 

 uervure or between the 2nd and 3rd or in one group, between the 1st and 

 2nd ; sectors of the arc generally with a longer fusion in the hind than in 

 the forewing ; 8th uervure generally from the anal anj^le of trigone 

 (separated in chrysostiyma and more or less in sahina) ; 12 to 21 antenodal 

 nervures (rarely more than 16 in Indian species); trigone in the hindwing 

 at the arc ; 1 cubital nervure to all wings ; no supplementary nervures to 

 the bridge ; trigone in the forewing high and narrow, its relation to the 

 hypertrigone generally more than a right angle, its anal angle basally 

 directed, traversed, in some species more than once ; trigone in the 

 hindwing long and narrow; its outer side moderately to strongly 

 concave, entire or traversed ; 4th nervure strongly undulating and 

 the end bent strongly to the termen ; 1 to 3 rows of cells between 5 

 and ^a ; 8th nervure in the forewing short and strongly convex ; the dis- 

 coidal field wide, a little constricted near its middle but strongly dilated 

 at the termen ; 3 to 4 rows of cells in the discoidal field ; loop well-deve- 

 loped ; its outer angle equal to a right angle and 4 or more cells distal to 

 the outer angle of the trigone, the apical segment longer than wide ; 3 to 

 tj rows of cells in the anal field ot hindwing. 



Stigma medium-sized ; membrane large. 



Abdomen variably shaped, moderately to very strongly dilated at the 

 base, then constricted or parallel-sided or fusiform or moderately broad 

 and depressed and gradually tapering to the end. 



Sexual organs of 1 he male : the lamina depressed or projecting, coated 

 with Btifl hairs or naked ; the tentaculte well-developed as a rule, the 

 internal segment furnished with a variably sized hook ; the lobe project- 

 ing or sloping, arched more or less and generally coated with stifl bristles. 



Sexual organs of the female : border of 8th abdominal segment dilated 

 as a rule but in several species not so or only slightly so ; no distinct 

 shape to the vulvar scale, generally notched and with a more or less 

 swollen border to the 8th segment ; ventral plate without any specific or 

 constant shape ; its styles distinct. 



The members of this genus present such remarkab e polymorphism and 

 polychroism, not only in the species but also amongst the individuals of 

 the species, that the task of forming any satisfactOj.y key is one of ex- 

 treme difficulty. The key given below is not entirely satisfactory but if, 

 where difficulty is met with, it be used in conjunction with the descriptions 



