PREDACEOUS WATER-BEETLES. 51 



fins. The larvne leave the water and make little cavities in the earth, 



when about to transform. Two hundred and thirty North American 



species have been described, arranged, lor the most part, in the fol- 

 lowing genera : 



A. Antenna? lO-.joiiited; hiiirt coxal plates greatly dilated, so as to cover I lalf of the abdomen; legs 

 slightly natatorial; size small; , form somewhat pointed before luid behind; color yellowish 



si)otted witli blackish Halii'LUS, 15. 



A A. Auteniiir 11-jointed; coxal plates obsolete ; legs strongly natatorial. 



B. Tarsi distinctly 5-jointed, not bilobed ; scutelluiii distinct (except in LaccophiUis). 

 C Anterior tarsi of males widened and forming a ronnded disk with cups beneath of very un- 

 equal size ; generally lai'ge or medium-sized insects. 



I). Hind tarsi with one claw ; size very large, exceeding an inch in length Cybister, 3. 



1> D. Hind tarsi with two claws. 



K. Claws equal, ov nearly so; size largo, or very large Dytiscur, 11. 



E E. Ulaws unequal. ' 



F. Body oval, depressed ; size about medium AciLlus, 6. 



1' F. Body elliiitical ; convex ; size below the medium Hyuaticus, 9. 



C C. Anterior tarsi of males widened, Avith the joints oblong and with cups of about equal size; 

 size usually below medium. 

 G. Scutellum distinct; length between a (piarter and a half of an inch. 



H. Hind claws unequal ; formless convex CoLYMHRTEa. 25. 



H H. Hind daws equal ; form more convex AciABUS, 47. 



G G. t^cntel wanting; hiiul legs stout, t<)m])r(ssed : length quarter of an inch or less ; 



Laccophilus, 9. 

 B B. Tarsi apparently 4-joiuted; third joint bilobed; scutellum wanting; size very small : 



HYUROrORUS, 91. 



Family IV. GYRINID.E. 



Founded upon the genus Gyrinus^ a name derived from a Greek word 



meaning a eircle, and given to these insects on account of their habit of 



Fig. 16. swimming round in little circles upon the surface of 



the water. The antenuie are very short and peculiar, 



and of the form called auriculate. The second joint 



is large and ear shaped, and the following ones form 



a short spindle-shaped mass. They are inserted in a 



little cavity in front of the eyes. The middle and 



hind legs are very short, scarcely reaching beyond tlie 



sides of the body, and very broad and tlat like little 



plates. These insects are of a medium or small si/.c, 



gyuinus:-!, beetle ; of a shluing blueblack color, and are often seen in 



% larva-after Packard, ^l^,^^^^, floykg playing and gyrating upon the surface of 



still water. Number of N. A. species, thirty-seven. 



