THE WHEEL ANIMALCULES (ROTATORIA) 619 



138 (i) Two ovaries Subclass Digononta. 



In fresh water; only one group Order Bdelloida . . 139 



Free-living. Swimming with the corona or creeping like a leech, or both. Body without 

 lorica, usually nearly cylindrical, dorsal and ventral surfaces not being conspicuously differ- 

 entiated, and composed of rings which may be drawn one within the other in telescopic 

 fashion. A dorsal proboscis behind the corona; jaws ramate (Fig. 867). 



139 (146) Corona present . 140 



140 (145) Corona of two nearly circular disks raised on short stalks, present- 

 ing the appearance of two wheels. 



Family PHILODINIDAE . . 141 



141 (144) Eyes, two , . ^ 142 



142 (143) Eyes in the dorsal proboscis Rotifer Schrank. 



Several species. 



Representative species (Fig. 958). . . Rotifer citrinus Ehrenberg. 

 (Fig. 960). . . . R. neptunius Ehrenberg. 



143 (142) Eyes in the neck, directly over the brain, just above the jaws. 



Philodina Ehrenberg. 



Several species. 



Representative species (Fig. 959). . . Philodina roseola Ehrenberg. 

 (Fig. 867, A, page 577). . . P. brycei Weber. 



144 (141) Eyes, none Cattidina Ehrenberg. 



The genus Callidina when revised will be broken into several genera. Many species. 



Representative species (Fig. 961). . Callidina angusticollis Murray. 



145 (140) Corona a flat surface covered with cilia on the ventral side of the 



anterior end. Family ADINETIDAE. 



One genus only Adineta Hudson. 



Representative species (Fig. 957) Adineta vaga Davis. 



146 (139) No corona Family MICRODINIDAE. 



The mouth has a group of cilia about it. 



One genus only Microdina Murray. 



Representative species (Fig. 962 and Fig. 867, B, page 577). 



Microdina paradoxa Murray 



