ROTIFERS. 207 



study. Very few of our American forms have been 

 investigated, and there is no one book in the English, 

 nor, so far as I know, in any other language, to which 

 the beginner can be directed for help. The American 

 " Wheel-bearers " form a large field which ought to be 

 cultivated. There is room for many discoveries, and 

 an opportunity to greatly add to the world's store of 

 scientific information. 



In using the following Key, the beginner must re- 

 member that the sheath of some of the Rotifers is very 

 often colorless and rather difficult to see clearly, un- 

 less it has particles of dirt or other matters adherent 

 to it. At other times it may be conspicuous. The 

 Key refers to only those forms included in this book. 



Key to some Genera of Rotifers. 



1. In a gelatinous or other kind of sheath (a). 



2. Not in a sheath, but growing in attached clusters. (<#). 

 # Free-swimming (e). 



. Clustered ; sheath soft, gelatinous, colorless. La- 



cinuldria, 1. 

 a. Not clustered ; sheath gelatinous (5). 



a. Not clustered ; sheath not gelatinous (c). 



b. With five long, erect, ciliated arms on the front 



border. JStep/ianoceros, 2. 

 >. With five clusters of many long, fine, radiating 



hairs on the front border. Floscularia, 3. 

 5. With two ciliary disks ; sheath tubular, often 



branched. Actinurus, 4. 



