PREDACEOUS WATEK-BEETLES. 



51 



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

 when about to transform. Two hundred and thirty North American 

 sjx'cies have been described, arranged, for the most part, in the fol- 

 lowing' genera : 



A. Anti'unjp lO-ioiuted; hind coxal plates greatly dilated, so a« to cover half of the abdonipn; legs 

 slightl.T natatorial; size small; , form soniowhat pointed hetbro an<l beliind : color yellowish 



spotted with blackislj II Ai.in.is, 15. 



A A. Anteniiii' 11-jointed: coxal plates obsolete ; logs strongly natatorial. 



15. Tarsi distinctly 5-jointed, not bilobed ; scutelluni distinct (except in Laccopliihis). 

 C. Anterior tarsi of hi-.ilo.s widened lUid forming a rounded disk with cups beneath of very un- 

 eiliial size; gi'neralVy largo or medium-sized in.sect-s. 



1>. Hind tarsi with one claw ; size very large, exceeding an inch iu length Cyhistek, 3. 



I) D. Bind tarsi withltwo claws. 



E. Claws equal, or nearly so ; size large, or very largo DvTisri's, 11. 



K K. Claws uneqiial. 



K. 15ody oval, depr&ssod ; size about medium Actl.U'H, fi. 



V V. Body elliptical ; convex'; size below the medium Hyuaticus, 9. 



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

 size usu:illy below medium. 

 G. Scutellum distinct ; length between a (luarter and a lialf of an inch. 



U. Hind claws nne(inal ; formless convex Cm. vmuries, ii. 



H U. Hind claws equal ; form more convex Aoabl's, 47. 



G G. Scutel wanting; hind legs stout, oomiircs.sed : Irnglh qiuii ter of an inch or less; 



LAltOI'HlLrs, 9. 



B B. Tarsi apparently 4-.ioiuted ; third joint bilobed; scutellum wanting i size very small ; 



HvuRoroRLs, 91. 



Family IV. GYKINID.E. 



Founded upon the genus Gyrinus, a name derived from a (Ireek word 



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



I'iK- 16. swimming round in little circles upon the surface of 



the water. The auteun:e 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 the 



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



plates. These inse(;ts are of a medium or small size, 



c.vuiMs;— 1, beetle; of a shining blue-black" color, and are often seen in 



2 larva-after Packard. ^^^^^^ ^^^^^^ playing and gyratiiig upoii thc surfuce of 



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



