186 Mr. O. Thomas on 



It was first obtained by the Antarctic Expedition of 

 ] 841-2 under Sir James Ross, and, later on, by the French 

 Cape Horn Mission, in whose Zoology (Mnridse written by 

 myself) it is referred to as " Re'ithrodon chinchilloides." I 

 owe to the kindness of Prof. Trouessart the loan again of the 

 adult specimen I determined in 1890, and the transference 

 by exchange of an immature example from the same 

 locality. 



The original specimen was^ unfortunately, put in some 

 peculiar preserving fluid, which has caused the skull, after 

 extraction, to shrink in drying. Its size, however, before 

 drying was quite the same as in the French specimen, and its 

 teeth are still unaff'ected. 



The OnrzoMYiS of the Extreme South of South America. 



When in 1881 I described " Hesperomys (Calomys) 

 copjnngeri^' no assertion as to the position of the type- 

 localities Cockle Cove and Tom Bay was made, but the 

 statement on the labels that these places were in the Straits 

 of Magellan was generally accepted, and influenced later 

 determinations. Now, however, on finding that all other 

 Oryzomys from the Straits region are referable to 0. magel- 

 lanicus, Benn., including those from Orange Bay, Cape Horn, 

 I have thought it probable that some mistake has been made. 

 On examining Dr. R. W. Coppinger's book, the "Cruise of 

 the ' Alert/ " 1883, it at once appears that Cockle Cove and 

 Tom Bay are not in what is commonly called the Straits of 

 Magellan at all, but are in Trinidad Channel, at the north 

 end of Madre de Dios Island, West Patagonia, in 50° S. lat. 



Since O. cuppingeri is so closely allied to O. magellanicus 

 as practically to diff'er from it in nothing but its greater size, 

 this location is far more natural than in the Straits, near the 

 centre of the range of 0. magellanicus. 



The specimens obtained by the French Transit of Venus 

 Expedition of 1882-3, named by me Hesperomys coppingeri^ 

 prove on re-examination to be typical O. magellanicus^ 

 wliich is evidently common throughout this region. 



But a series from further north, in middle Patagonia, 

 equally referable specifically to 0. magellanicus, prove to have 

 such uniformly longer tails as to deserve subspecific distinc- 

 tion^ as follows : — 



Oryzomys magellanicus mizurus, subsp. n. 



Size and other characters quite as in true magellanicus, 

 but the tail averaging about 130 mm. in length, in adults, as 

 compared with about 110-115 in the more southern form. 



