Animals of the Mississq^i^i Bottoms near Quincy. 165 



About .44 inch long, general color black, with front, sides 

 of thorax, and elytra yellowish brown. A line of this color 

 also across the middle of the thorax. This was the largest 

 beetle of its family taken at Quincy. It was captured in the 

 same locality as the larva preceding, and may prove to be the 

 adult, since the genera Acilius and Thermonectes are closely 

 allied. 



Locality, Cedar Creek. 



Family Gyrinid^. (Whirligig Beetles.) 



These are the shining black beetles so ofteu seen in large 

 numbers circling about on the surface of the water. The 

 three American genera all have representatives in Illinois. 

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

 since notwithstanding the 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 

 larvte 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. 



Gijrinus anab's, 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 frequently 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 water with surprising unanimity. 

 This evident knowledge of their whereabouts and ability to 

 take care of themselves on land was quite in contrast with 



