WATER BEETLES IN RELATION TO PONDFISH CULTURE. 



277 



The antennae extend obliquely outward and backward beneath the first and second legs; the maxillae 

 extend to about the center of the second legs; the labial palpi are longer, reaching the posterior margin 

 of the second legs. 



The femora of the first two pairs of legs are at right angles to the body axis, and the tibiae and tarsi 

 extend obliquely inward and backward to meet on the mid line. The third legs are similarly arranged, 

 except that the femora are pulled so far forward as to become diagonal to the body axis. 



There are large branches on the third legs for the spines at the distal ends of the tibiae. 

 ' ' The pupa is not very active in the pupal chamber and spends much of the time lying on its side. 

 However, the normal position seems to be with the dorsal side uppermost and the body strongly arched. 

 Of 10 pupae reared to the adult stage 7 emerged 4 days after pupation, 2 five days after, and 1 six 

 days after. 



Habits of the adult. — The adult beetle swims rapidly and with considerable agility, the tarsi of the 

 hind legs being especially well armed with swimming setae. When captured in the net, it proves to 

 be a good jumper, but can not equal Laccophilus and Thermonectes. On the land it can not lift its 

 body clear of the ground, and hence flounders around rather helplessly. The only food that any of the 

 adults were seen to eat was the nymphs of damselflies, but it is almost certain that their diet is not con- 

 fined to these. 



Description of the adult. — General shape an elongated oval, broadest anteriorly, the dorsal surface 

 subconvex; total length 7 mm., width 4 mm. 



The head, thorax, and entire under surface of the body are reddish-brown, the reddish tinge rather 

 brighter in the male. The vertex of the head is black, and the prothorax has a narrow black line across 

 the base and apex. The apical line stops on either side at about the center of the eye and does not reach 

 the lateral margin. The basal line is only half the width of the thorax and is slightly enlarged at either 

 end. The elytra are dark brown with numerous very small pale yellow markings. The basal portion 

 of the elytra in the female is not as shiny as in the male and is sculptured with short and indistinct 

 striae. 



The antennae are 11-jointed, joints about equal; the mandibles have a rounded tooth on the dorsal 

 surface of the inner margin near the tip and a fringe of short bristles behind the tooth. In the maxillae 

 the palps are four-jointed and subclavate, the terminal joint distinctly notched at the tip. The labial 

 palps are also notched at the tip, but the notch can be seen only in side view. The presternum is keeled 

 along the mid line and the process it gives off is swollen through the center. 



In the male the first three joints of the tarsus in the two anterior pairs of legs are slightly dilated and 

 furnished with a dense fringe of stiff hairs along the lateral margins, each hair tipped with a minute 

 disk. The ventral surfaces of these joints are covered with scattered disks, somewhat larger, each at 

 the tip of a long stalk whose diameter equals that of the disk. On the sides of the stalks and around 

 the margins of the disks are a few minute hairs. The tarsal claws are equal and so tightly appressed 

 laterally that they often appear as one; those on the front feet are long and emarginate at the base. The 

 hind legs are well developed, the femora with small laminae at the apex and the tarsi lobed externally. 



Genus CYBISTER Curtis. 



Cybister (Curtis, 1827, p. 151). 



This is a genus of large beetles considered the highest and most completely 

 developed of the dytiscids. Both the adults and the larvae are voracious and will 

 destroy young fish whenever opportunity offers. They have broad and powerful 

 hind legs and are strong swimmers; the hind claws are very unequal, the inner 

 one being obsolete or wholly wanting. In the males the front tarsi are strongly 

 dilated and bear four rows of disks. 

 Cybister fimbriolatus Say. Figures 23-33, 51. 



Cybister fimbriolaius (Say, 1825, p. 91). 



Cybister fimbriolatus (Sharp, 1882, p. 715). 



Cybister fimbriolatus (Duges, 1885, p. 26; pi. 2). 



Eggs. — Deposited singly in slits made in the stems of rushes, cat-tails, arrowhead, etc. The eggs 

 hatch in six to eight days. 



48790°— 23 4 



