36 BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



of individuals each nucleus is in a skein stage of mitosis, closely 

 similar to the same stage in P. intestinalis. The nuclei are thus seen 

 to be more advanced in mitosis in their internal structure than are 

 those of P. diplocarya, for though still pear-shaped they have their 

 macrochromosomes usually united into a skein. In individuals which 

 are entering upon fission there is no longer a thread connecting the 

 two nuclei. Each of these is much elongated and dumb-bell shaped, 

 and in each end of each dumb-bell are clearly seen four macrochromo- 

 somes. 



The species is very distinct from any other known form. 



PROTOOPALINA ACUTA (Raff). 



Opalina acuta Raff (1912). 



Host. — Limnodynastes dor sails (Gray), from Australia: One in- 

 fection observed by Raff. 

 Raff's description in full is : 



This other new species from Limnodynastes dorsaUs is much smaller than O. 

 dorsalis, and tapers very much toward the posterior end, forming a long tail- 

 like process. The average length is 257/i and the breadth at its widest portion 



Fig. 13. — Protoopalina actua. (After Raff.) 



of about 3Sai. The anterior nucleus is situated about 57jm from the front end 

 and the posterior about 10/* further on, and generally slightly nearer the 

 ventral [ !] sxirface. The cilia are well developed on the body portion, but 

 gradually diminish in size and number on the posterior process until for a 

 length varying from 25^ to 50/t from the tip of the process there appear to be 

 none. As the animal moves along, the anterior end is slightly raised, and the 

 dorsal surface appears flattened or straight, while the ventral surface is curved. 

 The characteristic feature that distinguishes this species from others Is the 

 very long, thin posterior portion. 



The description of Protoopaleria xenopodos (p. 61) should natu- 

 rally follow here, but is postponed because of certain comparisons of 

 nuclear conditions. 



PROTOOPALINA DORSALIS (Raff). 



Opalina dorsalis Raff (1912). 

 Host. — Limnodynastes dorsalis (Gray), from Australia. One in- 

 fection observed by Raff. 



Raff's description in full is as follows : 



The species of Opalina previously found in Limnodynastes dorsalis are 0. 

 [P.] intestinalis and 0. [Zelleriella] Mnucleata, the latter being a new 



