WATER-MITES AND THE WATER-BEAR. 267 



2. Body brightly colored, oval, or spherical ; legs eight, 



long ; animal swimming actively (a). 



3. Body brightly colored, oval, or spherical ; legs eight, 



long ; animal walking, never swimming (e). 



a. Ventral plate single, cordate, the apex pointing for- 

 ward. Diplodontus., 2. 



a. Ventral plate single, cordate, the apex rounded, 

 pointing backward (5). 



a. Yentral plate double (c). 



b. Posterior coxae on the same side not in contact. 



Hydrdchna, 3. 



c. Posterior coxae on the same side in contact by their 



whole length (d). 



c. Posterior coxae on the same side in contact only by 



their internal ends, their outer extremities di- 

 verging. Eyldis, 4. 



d. Yentral plates oval, with an oval plate on each side ; 



mouth round, with a circular hood. Arrenu- 

 rus, 5. 



d. Yentral plates narrow, curved, each with two or 



three translucent tubercles. Atax, 6. 



e. Eyes four, on a lanceolate plate; coxae in four 



groups. Limnochares, 7. 



1. THE WATER-BEAR: Macrobibtus (Fig. 172). 



The body -is soft, colorless, and transparent. The legs 



are very short, and have on the end of each several sharp 



claws, the legs being arranged three on each side of the 



body and two at or near the posterior, extremity. The 



