WATER BEETIJES IN RELATION TO PONDFISH CULTURE. 



285 



dark, olive-brown color of the fully matured adult. The shape is regularly oval, with the posterior 

 margin evenly rounded and not pointed as in Cybister; length 35 mm., width 20 mm. 



The clypeus is separated from the head by a distinct suture, the thorax is not margined, and the 

 claws are equal in both sexes. The elytra are smooth and do not show the numerous short impressed 

 lines found in the Cybister female. Near the posterior end of each is a narrow and oblique subapical 

 crossbar of yellow. The abdominal segments are uniformly black, and there are no yellow spots along 

 the lateral margins. 



In the male the enlarged tarsus of the front legs is nearly circular in outline and the sucking disks 

 on its ventral surface vary greatly in size. Near the base are two which are very much enlarged, their 

 combined diameters almost equaling the width of the swollen basal joint of the tarsus. The other 

 disks are smaller and rather irregularly arranged. 



Genus HYDROPORUS Clairville. 



Hydroporus (Clairville, 1806, p. 182). 



A genus of small species, all very similar to one another and hence difficult to 

 distinguish. The adults are oval in form and dark brown in color; they swim well 

 and when taken out of the water can jump quite a distance. The larv89 are spindle- 

 shaped and may be recognized by the fact that the head is much narrowed in front 

 of the antennae and the clypeus is prolonged into a sort of rostrum whose anterior 

 margin is armed with rows of wide laminge. The mandibles also are set at an angle 

 and shut up against the lower surface of the rostrum instead of shutting past each 

 other. 



Hydroporus niger Say. Figures 79-83. 

 Hydroporus niger (Say, 1825, p. 102). 



Eggs. — Nothing is known of how or where the eggs are laid or of the length of time that elapses 

 before they hatch. In the species whose larvae have been described by Schi0dte and Meinert nothing 

 was said about the eggs. 



Habits of the larva. — The larvae live among the Mougeotia and other filamentous algae, over which 

 they crawl almost ceaselessly. They swim very slowly, because their legs are short and have no swim- 

 ming fringes but only a few scattered setae. When out of the water they can walk quite rapidly, but 

 can not run or jump. The larva has no lateral gills and does not come to the surface for its supply of 

 oxygen, but is enabled in some way to obtain it from the water. It feeds upon the larvae commonly 

 found among the algae, such as Chironomus, Epiphragma, Odontomyia, Corethra, Probezzia, and Palpo- 

 myia. They do not appear to be cannibals and can be kept together in confinement without eating 

 one another, as was noted by Needham and Williamson (1907). 



Description of the larva. — General form spindle-shaped, narrowed only a little anteriorly, very 

 much posteriorly; length 7 mm., width 1.6 mm. Body made up of a head, three thoracic and eight 

 abdominal segments, widest through the mesothorax and metathorax, whose diameter is about one-fifth 

 of the body length, exclusive of the posterior cerci. The thorax and first six abdominal segments are 

 covered dorsally with chitin sclerites; those of the last two segments cover the lateral and ventral 

 surfaces as well as the dorsal. 



Color light brown on the dorsal surface, the head and the last two segments of the abdomen yellow; 

 a broad Y-shaped brown mark on the head, following the sutures; antennae, mouth parts, legs, and entire 

 ventral surface white, tinged with brown on the thorax. Each sclerite covers the whole dorsal surface 

 of its segment and is armed with setae along its lateral margins and a transverse row across its posterior 

 margin. The sclerites of the sixth and seventh segments are prolonged into small papillae at their pos- 

 terior comers. The lateral areas of the head and the rostrum are also covered with setae. 



Head ovate, one-half longer than wide, the clypeus prolonged into a broad and bluntly rounded 

 rostrum, extending far in front of the antennae. The top of the head and the rostrum are strongly convex, 

 and the tip of the rostrum is curved over ventrally. On this turned-down anterior margin is borne the 

 characteristic dytiscid fringe of this genus. In the present species it consists of three rows of flattened 



