ROTIFERS. 217 



genus by the extension of the front of the carapace 

 over the ciliary disk, like the visor of a boy's cap. A 

 not uncommon species is shown by Fig. 149, in side 

 view, so as to exhibit the long, movable bristle springing 

 from the back, and the curved visor 

 which, in the figure, looks like a line 

 above the frontal cilia. The Rotifer 

 is one of the nibblers. The mastax is protruded from 

 the mouth, which is near the front of the lower flat- 

 tened surface, and bites and tears the food it meets 

 with. It is often to be seen gliding over aquatic plants, 

 nibbling as it goes. The carapace is thin and quite 

 flexible. It extends over the sides of the body, so as 

 to give the Eotifer an ovate outline when seen from 

 above or below. The bristle on the back is very mov- 

 able and flexible. 



In one of the species the carapace is prolonged at 

 the posterior border into two lateral teeth. In another 

 this part is without teeth, and the dorsal bristle is also 

 absent, as it is in all the known American species, except 

 the one shown in Fig. 149. 



10. PTEBODfNA (Fig. 150). 



The carapace is almost circular, much flattened, and 

 perfectly transparent. The anterior border has a broad 

 notch with rounded margins, over which extends a lip 

 with a central rounded projection. The ciliary disks 

 are two, and rather widely separated. In the figure they 

 are shown retracted into the body. There are usually 



