THE OPALINID CILIATE IXFUSORIAXS, 



115 



This species resembles Z. hylaxena in form of body and in size of 

 nuclei. The individuals with resting nuclei are very similar and 

 could hardly be distinguished, though the endospherules of the latter 

 species are larger. But the nuclei of dividing individuals are very 

 different. In Z. Mjlaxena fission is consummated when the two nuclei 

 are each in a very constricted dumb-bell form, while in a similar 

 fission stage of Z. venezuelae the nuclei are ellipsoidal and wholly 

 unconstricted, a much earlier mitotic phase. As the nuclear phenom- 

 €na are the most fundamental in the speciation of the Protoopalinas 

 and Zelleriellas, I do not hesitate to recognise Z. venezuelae as a 



Fig. so. — Zellekiklla venkzuelae, X 460 diameters : c snows ax aljiost epce view 



OF THB ANTERIOR ENO AND AN OBLIQUE VIEW OF THE POSTERIOR END OP A TWISTED 

 INDIVIDUAL. 



distinct species, more archaic in < its nuclear character than Z. hylax- 

 <: na. It should naturally have been described before the latter species. 



ZELLERIELLA BINUCLEATA (Raflf). 



Opalina binucleata Raff (1911). 



Hosts. — Liinnodynastes dorsalis (Gray) and L. tastnaniensis Guen- 

 ther, both from Australia; Janet W. Raff, collector. 



I have had no material of this species. Raff's description in full 



is as follows : 



Opalina binucleata, n. sp. This is found in great numbers in Limnodijnnstes 

 dorsalis and on one occasion I met with it in L. tasmaniensis. It is a broad, 

 flat form with two nuclei, and is ciliated equally over all its surface, the 

 cilia being arranged in longitudinal rows as in other Opalinae. It is broader 

 and more bluntlj^ pointed at the posterior end than at the anterior [fig. 81o] 

 and moves along with the anterior end foremost. Its usual position Avhen 

 swimming along is on either flat surface, but as it proceeds it occasionally rolls 

 over from side to side. The average length is 157/^ and the average breadth 

 lOOfi, but larger and smaller individuals have been met with. When the 



