178 



Memoirs of the Indian Museum. 



[Voi,. V, 





Breeds in water 



General distribution. 





of sp. gr. 





Odonata 







Pseudagrion microcephalum 





i-ooi — i 4 oo8 



India and Malaysia. 



Rhynchota 











Euratas formidabilis 







rooo — 1/0265 



Bay of Bengal. 



Diptera 











Efistalis arvorum 







1-0035 — 1 '007 



Oriental region. 



Palpomyia sp 







i - 008 





Anopheles rossii 







i'ooo— 1/015 



Tropical and subtropical countries. 



Lepidoptera 











Nymphula diminutalis 







1 008 



Northern India to Celebes. 



Unlike the other groups of animals with which we have to deal in this volume , 

 the insects are for the most part immigrants from fresh water and drift or fly into or 

 on to the lake from the neighbouring ponds or rice-fields. Euratas formidabilis is 

 possibly the only exception, belonging to a marine group and having been taken at 

 sea in the neighbourhood of land. 



A phenomenon that exercises considerable influence on immigration in the case of 

 both surface-living and sub-aquatic species is the periodic growth and decay of a 

 weed of the genus Potamogeton that forms dense submerged thickets during the dry 

 season in certain sheltered bays of the main area of the lake, dying down almost 

 completely in the fC rains." The dry season is also the season at which the water of 

 the lake has the highest specific gravity, that is to say, is saltest ; but increase of sali- 

 nity seems to be of less importance than the existence of adequate shelter. The only 

 situation in which we found insect life at all vigorous was in thickets of this weed, in 

 water of specific gravity varying from i - ooi to i-oo8. Both submerged and surface 

 forms were abundant in or over the weed, the latter including Hebrus bengalensis , 

 Mesovelia mulsanti, Hydrometra vittata and several species of Gerris among the Rhyn- 

 chota, the former Micronecta proba, and Sphaerodema rusticum of the same order, as 

 well as a number of small beetles of the families Dytiscidae and Hydrophilidae, the 

 larvae and pupae of the flies Anopheles rossii and Palpomyia sp., of the moth Nym- 

 phula diminutalis and of the dragon-fly Pseudagrion microcephalum. 



The great majority of the aquatic insects of the lake are species of very wide dis- 

 tribution in the Oriental region, if they do not even extend beyond its borders. 



1890. 

 1900. 

 1902. 

 1904. 



Order ODONATA. 

 By F. F. L,aidi,aw. 

 Family Agrionidae. 

 Pseudagrion microcephalum (Ramb.). 



Pseudagrion microcephalum, Kirby, Cat. Odonata, p. 153. 

 >» ,, Ris, Arch. Naturgesch., p. 198. 



>> ,, Laidlaw, Proc. Zool. Soc. London, p. 388. 



,, ,, Martin, Mission Pavie, p. 18 (sep) 



