97 



double eyes (the margin of the head beinf? continued across them), 

 elongated fore legs and siiort, flattened middle and hind legs. 

 They secrete a milky fluid, which probably is offensive to fishes, 

 since notwithstanding tlie great numbers in which they occur, 

 they are very rarely eaten by other animals. The eggs are placed 

 in parallel rows on the leaves of plants in the water. The larvae 

 of European species are fully grown at the beginning of August, 

 and creep up rushes and spin upon these a papery cocoon. The 

 adult beetle emerges from this in about a month and returns to the 

 water, where it hibernates in the mud. In some cases the cocoon 

 is placed at some distance from the water, under the bark of trees. 

 The beetles are said to feed on dead insects. The larvse may be 

 known by their long slender bodies, the nine abdominal segments 

 of which are furnished at each side with long fringed respiratory 

 appendages. Tarsi with two claws. Posterior end of body with 

 four curved hooks. 



Gyrinus anal is, Say. 



(Say, Trans. Am. Philos. Soc, ii, 108, 1825; Compl. Writ., ii, 

 520,562.) 



A small Gyrinus which I presume to be this species was seen fre- 

 quently on the pools in immense swarms, often with a few specimens 

 of the larger Dineutes among them. When they were dipped up and 

 carried ashore they turned and began making their way back to 

 the Avater with surprising unanimity. This evident knowledge of 

 their whereabouts and ability to take care of themselves on land 

 was quite in contrast with the behavior, under similar circum- 

 stances, of the equally common water bugs of fche genus Corisa. 

 The latter, when brought ashore by the nets, scattered in every 

 direction, and few of them ultimately reached the water again. 

 The food. of those examined consisted entirely of fragments of in- 

 sects, which, judging by the large number of hairs, scales, and 

 fragments of legs, were from moths which had fallen upon the 

 water. Other species of Gyrinus from other parts of the State 

 have been found to contain similar matter, from which it seems 

 probable that they depend upon food of this character. 



Dhieuies assimilis, Aub6. 



{Cijclinus assimilis Kirby, Fauna Bor. Am. iv, 78, 1837; Dineutes 

 assimilis, Lee, Proc. Acad. Nat. Sci. Phil., xx, 366, 1868.) 



Two of three specimens examined contained fragments and scales 

 of moths; and the third had eaten fragments of small predaceous 

 land beetles, and an aquatic worm, — Lumbriculus, or of some allied 

 genus. The beetles are the common large whirligig beetles of 

 ponds and lakes everywhere in the State. They were common in 

 most of the pools at Quincy, and a few were noted sheltered 

 among the branches of a partly submerged tree that had fallen 

 into the swift current of the Mississipi River. 



F. C— 7 



