320 
BULLETIN OF THE BUREAU OF FISHERIES. 
metanotum with a single stylus on either side near the elytron and wing; scutellum prominent in the 
center of the mesonotum. 
Antennae inclined backward at an angle of 45° with the body axis, mandibles, and maxillae very 
prominent, the maxillary palps extending beyond the tips of the first legs. Basal joints of all three 
pairs of legs nearly at right angles to the body axis, tibiae of the first two pairs flexed back against them, 
tibiae of the third legs curved inward at an angle of 45°. Tarsi of the first legs flexed sharply 
backward, of the other two pairs nearly continuous with the tibiae ; tibial spines prominent on the second 
and third legs. Tergite of first abdominal segment with four styli; tergites of the second to seventh 
abdominal segments inclusive with six styli; eighth and ninth tergites with two each. Eighth stemite 
with a pair of appendages on its posterior margin, touching each other on the median line and extending 
backwards over the ventral surface of the ninth segment to the bases of the cerci. Posterior outer comers 
of the ninth stemite prominent and acute; cerci two-jointed, fleshy, tapering, 1 mm. in length. 
The duration of the pupal stage in 2 beetles whose larvae were brought into the laboratory and 
placed in artificial pupal chambers was 4 and 5 days, respectively. On first emerging, the entire beetle 
is dark gray, the antennae and mouth parts white, and the legs reddish-brown. The color darkens 
rapidly, the eyes first becoming black, then the elytra dark brown, and finally the thorax and head 
dark brown also. 
Habits of the adult . — The adults live wholly in the floating Edogonium, Hydrodictyon, and 
Spirogyra and have never been taken in a net while sweeping other parts of the ponds. They seem, 
however, to prefer the undersurface of the leaves of Potamogeton as a support for their egg cases, and 
only two of the latter were found among the algse. These beetles swim well and crawl about among 
the algse rapidly, but they can not jump or run. They feed apparently entirely upon the algse, and 
being common in several ponds and entirely harmless they furnish excellent fish food. 
Description of the adult . — This species is distinguished from others of the genus chiefly by the fact 
that the prostemum is distinctly carinated. The general form is elliptical, 4 to 4.50 mm. long and 1.60 
mm. wide. All the specimens obtained in the Fairport ponds were dark yellowish-brown, a little 
paler toward the margins, with the entire undersurface black. 
Antennse nine-jointed, the three terminal joints much enlarged, almost spherical and densely 
covered with fine hairs. The ninth joint is much larger than the eighth and the eighth larger than the 
seventh. The sixth joint is three times as wide as long, with a tuft of hairs on its outer distal comer; 
the first joint is sharply bent near the base. Mandibles short and stout, the tip at right angles to the 
basal portion; a secondary tooth ventral to the tip and on the inner margin a distal tuft of coarse 
straight spines and a proximal row of stout curved setae. In the maxillae the palps are very long, 
nearly twice the length of the body of the appendage, and the galea is armed with rows of curved 
blunt spines. The labial palps are very short and do not appear at all in the pupa, being concealed 
by the other mouth parts. 
Enochrus diffusus. (Leconte.) Figures 117, 119, 121, 123-125. 
Philydrus diffusus (Leconte, 1855, p. 371). 
Two egg cases were obtained from the same pond, 13B, as those of the pre- 
ceding species and also from the leaves of Potamogeton illinoensis. They hatched 
in seven days, and the young larvae were reared to a length of 4 mm.; but they 
could not be carried further, and no pupae were obtained. The identity of the 
larva, therefore, is not absolutely proved, but since only two species of this genus 
have ever been found in the pond after repeated search it is reasonable to refer 
the present specimens to the second species. 
Egg case . — The egg cases are considerably smaller than those of nebulosus and quite different in 
structure. Apparently a flat strip of silk 2.50 mm. long and 2 mm. wide is first spun and securely 
fastened to the undersurface of the leaf. Upon this 10 or 12 eggs are placed in a single layer and secured 
by strands of loose silk. Then another strip of silk is spun over the eggs and fastened around the edges 
to the first strip. And finally a short and wide fag 6 5 mm. in length is added. This is as wide as the 
6 See p.332. 
