346 BULLETIN 120. UNITED STATES NATIONAL MUSEUM. 



lian and South American Zelleriellas. Such modification as the 

 Opalinidae have undergone since the establishment of their funda- 

 mental character has been due probably in large measure to trends 

 within the Opalinids themselves rather than to environmental stimuli 

 and control. Orthogenesis, rather than natural selection, seems to 

 have been the chief factor in the evolution of the Opalinids. 



Summarizing the indications as to division 6 of the Cepedeas we 

 may say that apparently they evolved in India in the middle Creta- 

 ceous; that they spread to the Seychelles at about the time the 

 India-Ceylon-Madagascar-Africa bridge was breaking up (fig. 235), 

 for none of their members reached Madagascar or Africa ; that they 

 lived through the early Tertiary in the Indian island (fig. 236), 

 reaching Asia in the late Tertiary (fig. 237) when India became 

 joined to continental Asia; that during the late Tertiary or later 

 (fig. 238) they migrated to Formosa and Japan (and possibly to 

 Europe, G. hispanica)^ and that at the same time they spread to 

 America by way of Alaska. The Brazilian species probably wand- 

 ered southeastward from westernmost North America instead of 

 crossing early from Africa, for no Cepedeas of this division are 

 known from Africa. 



DNGEOUPED SPECIES. 



The remaining species of Cepedea are difficult to associate in 

 groups, for their affinities are not well indicated. Their geographi- 

 cal distribution is, therefore, of less interest to discuss. Cepedea 

 horneonensis (p. 159), of Borneo, may well be a recently evolved 

 species ; C. formosae (p. 160) , known from Hong Kong and Formosa, 

 could have passed between its present habitats at any time since the 

 middle of the Tertiary (fig. 237, p. 305) ; C. fujiensis (p. 159) 

 may have evolved in Japan very recently, since Japan separated from 

 the continent of Asia; the central American species, O. meoeicana 

 (p. 160), is of uncertain ancestry and does not disclose the geographi- 

 cal origin or migration of itself or its ancestors. 



Summarizing the indications as to the genus Cepedea we may 

 say that it apparently arose in India or in the Madagascar-India 

 ridge during the Jurassic or early Cretaceous, before Africa and 

 South America separated, but after Australasia had broken away 

 from Equatoria ; that it reached continental Asia from India in the 

 later Tertiary and then spread to Europe, eastern Asia, Japan, and 

 to the Western Hemisphere by way of Alaska. One of its South 

 American representatives apparently arose from immigrants from 

 Africa. 



The hosts and the geographical occurrence of the species of the 

 genus Opalina are given in the following table, in which the Opalinae 

 angustae are annotated [J.] and the Opalinae latae are annotated 



