THE WHEEL ANIMALCULES (ROTATORIA) 619 



138 (i) Two ovaries. ... Subclass Digononta. 



In fresh water; only one group Order Bdelloida . 139 



Free-living. Swimming witli the corona or creeping lilce 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 'Ehrtnhtxg. 

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



144 (141) Eyes, none Callidina Ehrenberg. 



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



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



14s (140) Corona a flat surface covered with ciha on the ventral side of the 

 anterior end. . . . ... Family Adinetidae. 



One genus only Adineta Hudson. 



Representative species (Fig. 957) Adineta vaga Dams. 



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. 



