WATER SCAVENGER-BEETLES. 
53 
The last genus is regarded by many as constituting the type of a 
small family distinct from the Parnid®. Most of these imperfectly 
aquatic insects are clothed with fine silken hairs which seem to have 
the property of shedding the water, and of enabling the insect to sur- 
round its body with a globule of air whilst clinging to the stones be- 
neath the surface; whereas the purely aquatic beetles, the Dytiscid®, 
the Gyrinid® and the Hydropbilid®, which have the faculty of swim- 
ming and of rising to the surface of the water whenever they need a 
fresh supply of air, have no such clothing. Forty-eight N. A. species 
are known. A synopsis of the Parnid® of the United States is given 
by Dr. Geo. H. Horn in the 3d. vol. of the Tran. Am. Ent. Society. 
Family VI. HYDROPHILIILF. 
| Fig. 17.1 
Hydro PIULU8 ft, larva of U. piccus, Linn.; <?, egg-ease; d. same opened showing arrangement of 
eggs ; c, pupa — after Blanchard : b . II. triangularis \ Say., natural size ; /, antenna: g, anterior tarsus of 
female ; h, same of malo, all magnified ; i, side view of the sternal spine — after Kiley. 
This family is named from the genus Hydrophilus, a word of Greek 
composition meaning a lover of water. They constitute a somewhat ex- 
tensive series of water-beetles, but less numerous and less eminently 
aquatic than the Dytiscidie. In swimming they move the hind legs 
alternately, whilst the Dytiscid® strike with them both together like a 
frog. Both of these families contain both large and small species, the 
largest being an inch and a half in length. Many of the larger species 
of Hydrophilidie have the sternum or breast bone in the form of a keel, 
and prolonged posteriorly to a sharp point. They are essentially dis- 
tinguished from the predaceous water-beetles by their short clavate an- 
tenme and their long palpi, which are usually longer than the antenmc, 
and are carried projecting forwards whilst swimming. The larvic of 
Hydrophilus are predaceous. The names of one hundred and twenty- 
two N. A. species are given in Dr. LeOonte’s catalogue, inclusive of 
twenty-one species of the small sub family of Sphroridiides. 
