106 Illinois Slate Lahonitonj of Natural Histonj. 



the behavior, under similar circumstances, of the equally com- 

 mon water bugs of the 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 insects, 

 which, judging by the large number of hairs, scales, and frag- 

 ments 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. 



Dineides assimilis, Aube. 



{Cijcliniis assimilis^ Kirby, Fauna Bor. Am., iv, 78, 1837 ; 

 Dlneutes 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 Qiiincy, and a few 

 were noted sheltered among the branches of a partly sub- 

 merged tree that had fallen into the swift current of the Mis- 

 sissippi River. 



Gyrinus, larva. 



A small larva about .25 inch long, from Wood Slough, 

 agrees exactly with published accounts of larvae of this genus. 

 Only one example was taken, though doubtless they were com- 

 mon, judging by the abundance of adult beetles. 



Family HyDROPHiLiD.i;. 



In the beetle state the food of this family is largely de- 

 composing vegetable matter. Occasionally the large species 

 attack mollusks or auiphibians. The larvio are carnivorous, 

 and, like those of the I)} tixida', do a good deal of damage in 

 fish ponds. They have a single tarsal claw. The labruni is 

 wanting. The 8th pair of spiracles is terminal, and the pos- 

 terior end of the body is devoid of hooks. Souie have fringed 

 appendages along the abdomen like those of Gyrinus larvio. 



