No. 2.] fRESH-WATER PROTOZOA. 65 



One species of Zoothamnium has been found, but no 

 figure of it has yet been made. 

 Opercularia Stein. 



Colonial, with stiff branched stalks which are often 

 ringed. Animals not bell-shaped, but ellipsoidal to ovate, 

 with a peristome not expanded. The ciliary disk upon 

 a long, thin stalk, around which a vestibule extends on 

 either side, closing like a lid. Nucleus short or ribbon- 

 like. One contractile vacuole. 

 Op. sp. (?), Fig. 297 a, b, c. 



CLASS SUCTORIA. 

 Key to Genera. 



1. Tentacles simple 2 



Tentacles branched; not retractile Dendrocometes 



2. No shell 3 



With shell 6 



3. No stalk 4 



Stalked, tentacles on all sides or in bundles. .Podophrya* 



4. Solitary 5 



Colonial, base branched with branching offsets whose 



swollen ends constitute the individuals. . .Dendrosoma 



5. Spherical ; tentacles on all sides Sphccrophrya* 



Irregular, fixed by a broad base ; tentacles in bundles 



Trichophrya 

 With a single movable anterior process instead of 

 tentacles ; parasitic on Cyclops Rhyncheta 



6. Shell unstalked, posterior end prolonged into a pro- 



jection ; attached to Epistylis; two to five long 

 movable tentacles Urnula 



Unstalked; disk- formed, tentacles in bundles 



Solenophrya 



Stalked, frequently enclosed by lobes in front. . . .Acineta 



Description of Genera. 



Sphaerophrya CI. & L. 



Without stalk; somewhat spherical, covered with 

 knobbed tentacles. Nucleus round or ellopsoidal. One 

 contractile vacuole. 

 5 



