THE OPALINID CILIATE INFUSORIANS. 321 



I 



than group 5: or in the early Cretaceous (fig. 234) while Java and 

 Australia were connected, spreading occurring from Java to Sumatra 

 and Formosa during the late Tertiary (fig. 237) or the Pleistocene 

 (fig. 238). 



Group 7 (fig. 245). 



P. regularis i p. 70 1 in Bufo tropical Africa. 



P. rhinodermatos (p. 71 ) in Gastrophrynidae South America. 



P. longinueleata (p. 72 i in Leptodactylidae South. America. 



P. bufonis (p. 74) in Bufo Cuba. 



The first three species of this group have an abrupt, short, un- 

 ciliated, spinelike, posterior process. Protoopdlina hufonis lacks 

 this spine, but the general shape of the body and the character of the 

 nuclei in detail are verj' similar to the conditions in the first three 

 species. Its relationship to this group seems probable. The occur- 

 rence of members of this group in tropical Africa and tropical 

 America suggests origin in South Atlantis, and the period would be 

 indicated as pre- Cretaceous or early Cretaceous (figs. 233, 234). 

 Their absence from Madagascar is not explained. The absence from 

 Australia would indicate a post-Triassic, that is, probably a Jurassic 

 origin (fig. 233). The presence of Protoofolina hufonis in Cuba, if it 

 be related to this group, as seems to be the case, confirms the evidence 

 from Zelleriella^ soon to be noted, that the West Indian lands were 

 formerly connected with continental tropical America (fig. 237). 



Group 8 (fig. 246). 



P. scaphiopodos (p. 76).in Scaphiopus (Pelobatidae) 



southwestern United States^ 



P. hammondii (p. 76) in Scaphiopus (Pelobatidae) 



southwestern United States. 



P. mexicana (p. 80) in Scaphiopus (Pelobatidae) 



northwestern Mexico. 

 P. mitotica (p. 77) in Ambystoma (Urodela) . west central United States^ 



This very compact, sharply distinct, and highly evolved group of 

 species have dumb-bell-shaped nuclei in a metaphase stage of mitosis. 

 The shape of the body is rather similar to that of P. intestinalis and 

 the group may be descended from immigrant ancestors from Euro- 

 Asia, which belonged to the intestinalis group. The occurrence of 

 one species in a Urodele is, of course, noteworthy. Except for this, 

 the species of the group are confined to one American genus, 

 Scaphiopus, itself similar to the Euro- Asian Pelohates, which bears 

 a Protoopalina {pelohatidis) of the intestinalis group. Euro- Asia 

 was probably the ancestral habitat of the Pelobatidae (fig. 224). the 

 American genus Scaphiopus having become but slightly modified 

 since its immigrant ancestor reached America, coming doubtless by 

 way of Siberia and Alaska. In Cretaceous times (figs. 234 to 235, A> 



