28 BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



cal and physiological nuclear phenomenon in the animal kingdom. 

 Indeed, we might well include the plants also in this statement. It 

 seems, therefore, clearly unwarranted to classify with the Opalini- 

 dae the astomatous Euciliates merely on the ground that they, like 

 the true Opalinids, have no ingestion apparatus. The latter quality 

 is doubtless due, in all these genera, to their life as parasites and is 

 a phenomenon of convergence rather than the result of genetic rela- 

 tionship. 



In the year 1918 ^^ I twice published a classification scheme as fol- 

 lows: 

 Ciliata 



Protociliata 

 Opalinidae 



Protoopalina 

 Opalina 

 Euciliata. 

 Further study of the material has shown that a truer expression of 

 the actual conditions is given in the following classification, which 

 is the one used in the present paper. The Opalinidae form an 

 appendage to the Ciliata which may be grouped as follows : 

 Ciliata 

 Protociliata 

 Opalinidae 



Pro toopalinmae 



Protoopalina '(cylindrical, or slightly flattened, 



binucleate forms) 

 Zelleriella [new genus] (much flattened, binucleate 

 forms) 

 Opalininae 



Cepedea [new genus] (cylindrical or slightly flat- 

 tened, multinucleate forms) 

 Opalina (much flattened, multinucleate forms) 

 Opalinue angustae {ocddentales) 

 Opalinae latae (orientales) . 

 Euciliata 

 The new genus Zelleriella is named for Ernst Zeller, who in 1877 

 published an excellent paper upon the species of Opalinidae then 

 Imown. The new genus Cepedea is named for Casimir Cepede, whose 

 studies of astomatous Ciliata have emj^hasized the fundamental dis- 

 tinction between true Opalinidae and other Ciliata. 



The four genera of Opalinidae are reasonably distinct, not inter- 

 grading to the point of rendering the line of demarcation doubtful. 



i^Metcalf, 1918 a and 6. 



