No. 6 (1917) A NOTE ON TREATMENT OF SWAMPS, ETC. 169 



Another larvicide common in stagnant waters is the Notonecta 

 glauca. 



The young of most of the fresh water indigenous fishes of India 

 attack and destroy mosquito larvje : but as some grow to a large 

 size they are only useful during the fry stage. In selecting the best 

 of the larvicides it is only necessary to include those that rely 

 chiefly on the larvee for their food supply it being their natural 

 diet. The following selection will be found a very useful one, the 

 geographical distribution of each genus being widespread: — 



For TANKS, BIG PONDS AND SWAMPS THE FOLLOWING ARE 



MOST SUITABLE, VIZ.— 



Genus-Chela. 



Desc/'il>tioii of grniis (Dr. Day) — Body elongate and compressed : 

 abdominal edge cutting. Mouth directed somewhat upwards with 

 the lower jaw prominent. Barbels absent. Pharyngeal teeth 

 hooked and slender, in two or three rows. Dorsal fin short, without 

 any osseous ray, situated principally or entirely opposite the anal, 

 which latter has an elongated base. Pectorals long. Caudal 

 forked. Scales of moderate or small size. Lateral line concave. 



Geographical distribufioi (Dr. Day) — Sind, Continent of India, 

 Burma, and extending to Malay Archipelago. 



These fish are surface feeders and their chief diet consists of 



flies and larvse. (All species good, the smaller ones being the 



best.) 



Genixs-Rasbora. 



Description of genus. — Abdomen rounded. Cleft of mouth obli- 

 que, lower jaw slightly prominent, having one central and on either 

 side a lateral prominence, fitting into corresponding emarginations 

 in the upper jaw. Barbels two (rostral) or none. Eyes with free 

 lids. Pharyngeal teeth. Dorsal fin without any osseous ray and 

 few branched ones, inserted posterior to the origin of the ventral, 

 but not extending to above the anal, which latter is short. Scales 

 large or of moderate size. Lateral line concave continued to the 

 middle or lower half of the caudal fin. Gill rakers short. 



Geographical distribution. — Africa, India, Ceylon, Burma to the 



Malay Archipelago. 



All species. 



Genus-Barilius. 



Description of genus. — Abdomen rounded. Mouth anterior, some- 

 times oblique, having a moderate or deep cleft. Jaws compressed. 



