WATER BEETLES IN RELATION TO PONDFISH CULTURE. 
295 
Description of the pupa . — The pupa is white in color, except the eyes, which are dark reddish- 
hrown and the face, which has a reddish tinge (fig. 69, p. 297). It is 8 mm. long, including the caudal 
cerci and 5 mm. wide. It is obovate in outline and quite strongly depressed. The segmentation is 
distinct and is rendered more conspicuous by the rolling up of the posterior margin of each segment 
into a ridge, which is low and flat on the ventral and lateral surfaces but stands out prominently on the 
dorsal surface, being highest at the mid line. The prothorax projects forward around the base of the 
head and carries on its frontal margin a fringe of long hairlike styli. On each lateral margin is a short 
process armed with five spines, and on each side of the dorsal mid line is a group of three stout styli. 
On the dorsal surface of the second thoracic segment are three spinelike styli on either side near the 
anterior margin and close to the mid line. On the third segment are four similar styli near the anterior 
margin, three near the posterior margin, one on the posterior margin near the base of the wing, and 
another near the mid line, nine in all on each half of the segment. On each of the first four abdominal 
segments are three large isolated styli on either side of the mid line along the posterior crest and one at 
the side of the segment behind the spiracle. The fifth segment has only two near the mid line and one 
behind the spiracle; the sixth and seventh segments carry a single pair of stout clawlike styli on the 
mid line and one behind the spiracle. The eighth segment has a compound handlike spine with three 
fingers on each lateral margin anteriorly and a single spine posteriorly. Its ventral surface is split 
back at the center, and the rudimentary ninth segment protrudes a pair of caudal cerci, short, stout, 
and bifid at the tip. When the pupa is on its back, all these styli and spines help to keep it above 
the earth floor of the pupal chamber. 
The antennae lie along the front margins of the elytra, and the maxillary palps extend straight back- 
ward beyond the tibiae of the first legs. The femur of the first legs stands at right angles to the body 
axis, and the tibia is folded back tightly against it; the two tarsi are parallel to the body axis and well 
separated. In the second legs the tibiae and femora are at right angles to each other, and both at an 
angle of 45° to the body axis; the tarsi are parallel to the axis and only slightly separated. In the 
third legs the tibiae and femora are arranged like the second pair, but the tarsi are in line with the tibiae 
and meet on the mid line. The time spent in the pupal stage is four or five days; two larvae were taken 
from the pupal chambers they had constructed on the shore of pond 5D on July 6 and placed in artificial 
mud cells; they pupated July 7, and the adults emerged July 11. A male pupa reared in August, 1921, 
remained six days in the pupa stage. 
Habits of the adult . — The adults swim with an even rapid motion, the posterior legs being the chief 
propelling organs. They rest at the surface with the posterior legs extending out at right angles from 
about the center of the body and the posterior end of the abdomen elevated above the surface film. 
When out of water, they move with considerable agility and can jump well, though not quite as vigor- 
ously as the following species. As indicated in the table, this is one of the rarer species, and it was 
fortunate that its life history could be seemed. 
Description of the adult . — General form elliptical in outline, a little broadened anteriorly and more 
pointed posteriorly, with a length of 10 mm. and a width of 6 mm. In the female the transverse yellow 
bar on the thorax is enlarged and turned diagonally backward at either end but does not meet the 
yellow on the lateral margins. In the male it is not enlarged or turned backward at the ends and it 
does meet the yellow margin. In both sexes the elytra are black with a transverse row of spots near 
the base and a wide margin yellow. The black is not an even wash of color but is made by many small 
black dots, more or less confluent. 
The antennae are 11-jointed, all the joints about the same length and width, except the basal one, 
which is lengthened at the expense of the second joint. Joints 3 to 7 each carry a small seta on the 
outer margin at the tip, and joints 3 to 11 have a sensory papilla on the inner margin near the distal end. 
The mandible is very thick, with a blunt emarginate tip, ending in an acute point at the ventral comer 
and a rounded tooth at the dorsal comer. The maxillae are well developed with long, four-jointed palps; 
the labial palps are also long but only three-jointed and emarginate at the tips. The tip of the second 
joint develops broad dorsal and ventral wings, armed with sensory papillae, on the inner margin. 
In the males the front tarsi are broadly dilated and bear three larger basal disks and numerous smaller 
unequal ones. The basal joint carries the 3 large ones and 5 smaller ones, the second and third joints 
carry 6 each, all small but unequal in size. The largest basal one is twice the diameter of the other 
two, and they in turn are twice the size of the smaller ones. The fringing hairs are evenly developed 
and are not interrupted at the point where the tarsus joins the tibia (fig. 67, p. 292). 
