I9I5-] 



Fauna of the Chilka Lake : Aquatic Insects. 



179 



L*l 



A. 

 B. 

 C. 



B. 



Fig. 1. — Pseudagrion microcephalum (Ramb.). 



Apex of abdomen of male, from above. 



Pattern on dorsum of 2nd abdominal segment of male. 



" Mask" of larva. 



Adult specimens have been examined from off Balugaon and Barkul on the 

 Chilka Lake ; the majority were taken in March, but I understand that the species is 

 common at all times of the year. Others are from Balighai on the Sar Lake in the 

 Puri district of Orissa and from Calcutta. Larvae and larval exuviae were sent 

 both from the Chilka Lake and from 

 the Museum tank, Calcutta, in several 

 cases with adults which had been 

 reared in an aquarium. 



The species is evidently very abun- 

 dant in Bengal and Orissa. I believe 

 it to be the true P. microcephalum of 

 Rambur. To facilitate identification 

 I have figured the terminal part of the 

 abdomen of the male, as seen from 

 above, and also the colour pattern of 

 the dorsum of the second abdominal 

 segment of the same sex (text-figs. iA, B). The superior anal appendages of the 

 male are about equal in length to the tenth segment, whereas in the closely allied P. 

 australasiae the corresponding appendages are not more than one-half the length of 

 the segment, and differ in shape. 



The colouring of young males of P. microcephalum is identical with that of the 

 females. 



Larva. — Very similar in general to that of European Erythromma najas (Hause- 

 mann). Body slender, of a pale sandy gray colour. 



Total length at time of emergence about 22 mm., of this the caudal lamellae 

 take up about 8 mm. 



Head pentagonal, antennae 7-jointed. Mask long (text- fig. iC), its anterior border 

 gently rounded, extending when folded beyond the insertion of the second pair of 

 legs. Its outer margin carries a few small spines, and there is a single large seta on 

 either side of the body. The palpi bear four stout setae directed inwards and the 

 movable hooks are long and overlap (text-fig. iC). 



The caudal lamellae have nearly parallel sides and are bluntly rounded at their 

 apices. Each is divided into two parts at about its middle by a transverse fold or 

 joint. Of these two parts the proximal has its margins spiny and there is a distinct 

 notch on the lower margin (of the lateral lamellae) between the proximal and distal 

 parts. The last spine on either margin before the transverse fold is the largest of 

 the series. The apical part has its margins smooth. 



There are two main tracheal trunks in each lamella. These cross and recross one 

 another ; their branches are arborescent near the margins and are marked with a 

 dark brown colour giving the lamella a mottled appearance. 



The larvae from Lake Chilka were collected in water which was distinctly brack- 

 ish, the specific gravity (corrected) of the water being roo8. I believe no Agrionid 

 larva has been recorded from brackish or salt water. Amongst the Libellulinae 



