PREDACEOUS WATER-BEETLES. 
51 
fins. The larva 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, for the most part, in the fol- 
lowing genera : 
A. Antenna? 10-join ted ; hind coxal plates greatly dilated, so as to cover half of the abdomen; legs 
slightly natatorial; size small; .form somewhat, pointed before and behind; color yellowish 
spotted with blackish Haliplus, 15. 
A A. Antenna* 11 -jointed; coxal plates obsolete ; logs strongly natatorial. 
B. Tarsi distinctly 5-jointed, not bilobed ; scutellum distinct (except in Lacoopliilus). 
C. Anterior tarsi of m.ilos widened and forming a rounded disk with cups boneath of very un- 
equal size; generally large or medium-sized insects. 
I). Hind tarsi with one claw ; size very large, exceeding an inch in length Cybistek, 3. 
I> D. Hind tarsi with two claws. 
K. Claws equal, or nearly so; size largo, or very large Dytibcus, 11. 
E E. Claws unequal. 
F. Body oval, depressed; size about medium Aciliub, 6. 
F F. Body elliptical ; convex ; size below the medium Hydaticus, !). 
C C. Anterior tarsi of males widened, with the joints oblong and with cups of about equal size, 
size usually below medium. 
G. Scutollmu distinct ; length between a quarter and a half of an inch. 
H. Hiud claws unequal ; formless convex Colymbrtes, 25. 
PI H. Hind claws equal; form moro convex Agabfs, 47. 
G G. Sc ut el wanting; hind legs stout, compressed : length quarter of an inch or less : 
« LACCOPH1LU8, 9. 
B B. Tarsi apparently 4-jointed; third joint bilobed; scutellum wanting; size very small: 
HYDBorORUH, 91. 
Family IV. GYRIN1D.E. 
Founded upon the genus Gyrinus, a name derived from a Greek word 
meaning a circle, and given to these insects on account of their habit of 
swimming round in little circles upon the surface of 
the water. The antennae are very short and peculiar, 
and of the form called auriculatc. 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 flat like little 
plates. These insects are of a medium or small size, 
i»>oi,ie ; of a shining blue-black color, and are often seen in 
dense flocks playing and gyrating upon the surface of 
still water. Number of N. A. species, thirty-seveu. 
Oykinuh: — I 
", larva — after Packard. 
