36 Journal New York Entomological Society. [Vol. xxi. 



PscpJicuus larva was in fact described by DeKay as a Crustacean. 

 The larvae of the other families crawl along the bottom or on stems of 

 aquatic plants, feeding on animal food in the Dytiscidse, vegetable 

 or mixed food in the other families, filamentous algse in the Hali- 

 plidse according to Matheson. The breathing apparatus is modified in 

 these larvae, usually tracheal extensions from the apex of the body, 

 permitting of the creature's drawing a supply of atmospheric air by 

 resting head down at the surface with these appendages protruding 

 above the surface. In the larvae of Gyrinidae such appendages pro- 

 ceed from all the segments except those bearing legs, so that the 

 larva has somewhat the appearance of a centipede. In the larvae of 

 some Haliplid^e, the air supply, according to Matheson, is obtained by 

 means of numerous long-jointed tracheated spines. The larvae of 

 Cncmidotus are illustrated by Schiodte with two long slender lateral 

 filaments proceeding from each segment, and with four recurved 

 hooks on the anal segment, which would assist the larvae in maintain- 

 ing its hold on plants. The larvae of Psephenus have been described 

 in detail by Kellicott, in the Canadian Entomologist. They are 

 almost circular and have waving extensions from the different seg- 

 ments. Among the Elmidae, the larvae of some species live in the 

 exceedingly soft mud of the banks of streams and have been studied 

 by Dufour and other foreign authors. In the larvae of Donacia 

 the eighth segment is provided with two spines apparently used for 

 piercing the air cells of aquatic plants. 



In general the larvae of aquatic beetles may be said to be modified 

 in respect of respiratory apparatus but otherwise they greatly re- 

 semble terrestrial larvae. 



Environment. 

 The interesting fact in connection with such aquatic Coleoptera is 

 that each requires more or less absolutely a special environment for 

 its development. In the cases in which it is insistent upon a particular 

 environment, it becomes rather rare from the scarcity of the con- 

 ditions it craves. Among the Dytiscidae, for example, we find Aga- 

 bctcs acuductus only in small woodland pools, with many fallen de- 

 caying leaves. In the water itself of such pools this species is likely 

 to be missing, but crawling among the submerged rotting leaves 

 near the edge of the pond they may be found, probably hunting some 



