608 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 87 



There are some features of the distribution that deserve the em- 

 phasis of special mention: (1) No multinucleate opalinids occur in 

 Australasia; (2) Cepedea does not occur in eastern North America; 

 (3) Protoopalina also is lacking in this area; (4) Protoopalina is 

 wholly, or almost wholly, absent from lands once parts of Lemuria; 

 (5) Zelleriella has never been in the Eastern Hemisphere north of 

 Australasia. Reasons for these conditions can be given: (1) Multi- 

 nucleate opalinids evolved in the Northern Hemisphere too late 

 to find any route to Australasia; (2) no Anura, apparently, have 

 crossed westward from Europe to America, the Greenland-Labrador 

 strait not having been bridged, at least at any time when climatic 

 conditions favored the presence of anurans in that region; (3) a far 

 from wholly satisfactory reason for the absence of the primitive genus 

 Protoopalina from Lemurian lands may be in the disturbances in land 

 and ocean levels in the Indian Ocean and the final breaking up of 

 Lemuria into several independent portions; (4) Zelleriella evolved in 

 Patagonia too late to find a route to the Eastern Hemisphere, 

 except to Australia.^" 



In former studies of the Opahnidae I have traced their evolution 

 in two main lines: (1) From Protoopalina through Cepedea to Opalinae 

 latae and finally to Opalinae angustae, and (2) from Protoopalina 

 directly to Zelleriella. The former named evolution was in the 

 Eastern Hemisphere, from Protoopalina to Opalinae latae, while the 

 last step, from Opalinae latae to Opalinae angustae, was in the Western 

 Hemisphere and occurred since the middle Pliocene. The second 

 named evolution occurred in greater Antarctica and later in tropical 

 America. Apparently the evolution of Zelleriella took place later 

 than the evolution of Cepedea and Opalinae latae, but before that of 

 Opalinae angustae. There is no indication of the derivation of 

 Opalina from Zelleriella. In the first line of evolution, the develop- 

 ment of multinucleation occurred first and then flattening was em- 

 phasized. In the second evolution only flattening is found, multinu- 

 cleation not developing. No reason is apparent why multinucleation 

 might not have followed rather than preceded flattening. That the 

 phylogeny described is correct is confirmed by the geographic distri- 

 bution of the several genera in the family: Protoopalina and Cepedea 

 occur together in the Eastern Hemisphere; Cepedea and Opalinae 

 latae also; Opalinae latae and Opalinae angustae occur together only 

 in North America, excepting the late emigrant to Euro-Asia, 0. 

 ohtrigona. On the other hand, Zelleriella and Opalina occur together 

 only in southern North America which was invaded by Zelleriella 

 long after Opalina had been evolved in Asia. 



There is probably no group of organisms known in which the course 

 of their evolution is more clearly, if as clearly, shown than it is in the 



w Since this was first written, knowledge of certain facts makes it questionable, e. g., Zelleriellas are said 

 to be in China (Nie, 1935). 



