WATER BEETLES 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 Cy bister; 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 larvae 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 laminae. 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 
