ZooL.— Vol. III.] HELLER— GALAPAGOS MAMMALS. 237 



Range. — Cosmopolitan in temperate and tropical regions. 

 Indigenous in western Asia. Galapagos Archipelago: 

 Albemarle Island (Baur, Hopkins Expedition), James 

 Island (Darwin, Hopkins Expedition), Chatham Island 

 (Hopkins Expedition), Charles Island (Hopkins Expedi- 

 tion). 



Galapagos specimens show somewhat shorter tails than 

 typical alexandrinus, but, as in that species, the annuli on 

 a perfect tail are usually about two hundred forty in num- 

 ber. The tail is much less hairy, the tympanic portion of 

 the skull is conspicuously larger, and the coloration of the 

 upper parts is less reddish than in decmnanus (norvegicus), 

 to which species Allen referred his mummified specimen. 



Specimens from James Bay, James Island, are larger 

 and more uniform in coloration than those from any of the 

 other islands. Albemarle specimens average small. Those 

 secured at Tagus Cove, Albemarle, are lighter above and 

 more sulphur-yellow below. Specimens from the moist 

 portions of the archipelago, as Iguana Cove, Albemarle 

 Island, and Wreck Bay, Chatham Island, are dark and 

 approach or intergrade in coloration with Mus rattus. 



The skulls agree essentially with those of Mus rattus. 

 They differ considerably from California and Cocos 

 Island^ specimens of Af. norvegicus. The tympanic bullce 

 are larger and not so far apart, the basi-occipital and basi- 

 sphenoid bridges being considerably narrower. 



This is the most abundant rat wherever it occurs. It 

 ranges widely, occurring from sea-level to the rims of the 

 highest craters. 



1 Four specimens oi M. norvegicus were taken at Cocos Island, July 3, 1899. These are 

 similar in coloration to continental forms, but are somewhat smaller. The largest male 

 measures: Total length 393 mm., tail vertebras 183 mm., hind foot 35 mm., ear 20.5 mm. 



