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CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



island of the group was visited, and collections of the fauna 

 and flora were made at each one. A special effort was 

 made to obtain all the species of indigenous terrestrial 

 Mammalia. 



Faunal Derivation. 



The affinities of the Mammalia appear to be entirely with 

 South American forms. Nesoryzomys, the only peculiar 

 genus, is most closely related to 07yzomys. The affinities of 

 the two species of Oryzomys which occur in the archipelago 

 are not yet known or determined, but the genus is chiefly 

 Neotropical. The single species of Lasiurus is very closely 

 allied to a Chilean species. The hair-seal Otariais a wide- 

 spread species of antarctic derivation, reaching its northern 

 limits in the Galapagos Archipelago. The fur-seal Arcto- 

 cefhalus is a peculiar species, but is evidently of antarctic 

 derivation also, its affinities being with A. fhiliffi of 

 Juan Fernandez. A South American derivation of the 

 Mammalia south of the Equator would be favored by the 

 direction of the existing ocean currents and winds, and it 

 is probable that these agencies are responsible for the 

 present distribution of mammals on the islands. The 

 evidence, however, of the relationships of several other 

 groups, especially the birds and flora, favors a Central 

 American derivation with only a slight South American 

 element; but this may be due to the greater antiquity of 

 such forms in the archipelago. 



Distribution. 



The genera Oryzomys and Nesoryzomys are known only 

 from Chatham, Barrington, Indefatigable, Seymour, and 

 Narborough islands. Leaving out of consideration' Albe- 

 marle, James, Charles, and Duncan, the islands which are 

 inhabited by introduced species, it seems remarkable that 

 large islands like Abingdon, Bindloe, and Hood should lack 

 indigenous species of Muridae. A careful search, however, 

 failed to discover any mammals on these islands. It is 



