THE OPALINID CILIATE INFUSORIANS. 467 



all genera of Opalinidae. ProtoopaUna mexicana belongs to the 

 group of species characteristic of Scaphiopus and they were appar- 

 ently developed in North America from an ancestor immigrant from 

 Asia by way of Alaska. The other Protoopalina is a southern form 

 intermediate between the genera Protoopalina and Zelleriella. The 

 four Sonoran Zelleriellae are, of course, immigrants from further 

 south. Of the two Sonoran Gepedeae one is of uncertain affinities; 

 the other, from a Texan Hyla^ seems to belong to a group containing 

 eastern Asian and Malaysian species, a group not represented in 

 northern Asia. The Opalinae are chiefly Western Hemisphere nar- 

 row species, though we find in 0. gigantea an immigrant represen- 

 tative of the Eastern Hemisphere broad species. 



On the Pacific coast we find no Protoopalinae. Well to the south 

 are two Zelleriellae., evidently immigrants from further south. No 

 ■Gepedeae are present. The Opalinae are narrow species except for 

 O. draytonii, a broad form immigrant from eastern Asia. 



From tropical Central America we know but a single Protoopa- 

 lina, xyster, one of the two species which show transition toward the 

 genus ZelleHeUa. The Zelleriellae are abundant, eleven species 

 being known, tropical America being the present major habitat of 

 the Zelleriellae. Of the four Gepedeae two {glohosa and haudinii) 

 show African affinities and are probably derived from ancestors im- 

 migrant from Africa by way of the Guianas, while the two other 

 species belong, one to a group with mostly Asia-Malaysian species, 

 and the other to a group represented both in Asia-Malaysia and in 

 the Seychelles Islands, the latter occurrence being a puzzle and re- 

 quiring further study. The Opalinae are narrow forms, except one 

 which is broad and two which intergrade between the narrow and 

 broad groups. 



The West Indian species show tropical continental American affin- 

 ities. The Protoopalina, hufonis, seems to belong to a group with 

 both African and South American representatives and which we re- 

 garded as having arisen in South Atlantis. The four Zelleriellae 

 are, of course, tropical American. No Gepedeae nor Opalinae are 

 known from the West Indies. 



Northern and northwestern South America shows one Protoopalina 

 and nine Zelleriellae. 



From eastern Brazil we know no Protoopalina and of course no 

 Opalina. There is one Zelleriella, found also further south, in 

 Argentina. The only known Gepedea is found in Central America 

 and we have regarded it as belonging to a group with chiefly Asia- 

 Malaysian species, though the same group shows apparently one 

 representative in the Seychelles Islands and possible one in Spain. 

 This group is but a loosely affiliated one showing a rather wide 

 range of intergrades from the dirmdiata-like forms toward the longa 

 forms. 



