Vol. XII, pp. 13-19 January 27, 1898 



PROCEEDINGS 



OF THE 



BIOLOGICAL SOCIETY OF WASHINGTON 



MAMMALS OF TRES MARIAS ISLANDS, OFF WESTERN 



MEXICO. 



BY C. HART MERRIAM. 



Mr. E. W. Nelson spent the month of May, 1897, on the Tres 

 Marias Islands in the interest of the Biological Survey of the 

 U. S. Department of Agriculture. This visit has resulted in a 

 la rue increase in knowledge of the fauna and flora of the islands. 

 The new birds are described b} r Mr. Nelson in a preceding bro- 

 chure of the present volume; the new mammals are named in 

 the present paper. 



In the Mammal volume of the ' Biologia Centrali-Americana ' 

 it is stated that according to Mr. Forrer, a collector who visited 

 the islands in 1881, only three indigenous land mammals, be- 

 sides bats, occur there. These are a rabbit, a raccoon, and a 

 pigmy opossum. Mr. Nelson obtained all of these and two addi- 

 tional genera, a rat (Oryzomys) and a white- footed mouse (Per- 

 omyscus), and these in spite of Mr. Forrer's statement that "the 

 inhabitants know of no rats or mice whatever in the islands, 

 except, of course, the cosmopolitan Mas decumanus " (p. 212). 

 The introduced rat brought back by Mr. Nelson is not the com- 

 mon or Norway rat (Mus decumanus), but the Roof rat or gray 

 phase of the Black rat (Mas rattus). 



Mr. Nelson and his assistant, Mr. E. A. Goldman, collected 146 

 specimens of mammals, representing nine species, of which the 

 introduced rat is one, three are bats, and five are indigenous ter- 

 restrial land mammals. Of the latter, the rabbit is peculiar to 

 the islands, and was described by Allen in 1877 ; the remaining 

 four I have compared critically with the most closel}' related 



3— Bior.. Sue. Wash., Vol. XII, 1898 (13) 



