ALLEN: mammalia: murid^. 45 



northern United States, being blackish oHve gray instead of black, but it 

 can be matched exactly in specimens of corresponding age from Jupiter 

 Inlet, Florida, and from the Island of Trindad, B. W. I., but in both cases 

 these specimens are Mus rattus more or less mixed with M. alexandrimis, 

 to which category the Punta Arenas specimen doubtless belongs. 



The Black Rat [Mus rattus Linn.) and the White-bellied or Roof Rat 

 {Mus alexandnnus Geoffroy) are widely dispersed in the warmer parts of 

 America, and at many localities hybridize freely, so that specimens of pure 

 strain of either species are rare. In the northeastern United States the 

 Black Rat was formerly an abundant inhabitant of houses and outbuildings 

 in the farming districts, while the Brown or Wharf Rat [Mus norvegicus 

 Erxleben = il///5 decunianus Pallas) swarmed in the cities, particularly 

 about wharves and in warehouses. The latter is not only larger and more 

 powerful than the black rat, but antagonizes it, and has to a large extent 

 driven it out or exterminated it in the New England and Middle States 

 of the Union. In the South Atlantic States the Roof Rat has long 

 been the prevailing species, where it seems to have become widely dis- 

 tributed. 



From Mexico, Central America and in northern South America both M. 

 rattus and M. alexandrinus are often received in collections, being caught 

 in traps, in fields and wooded areas remote from settlements, by collectors 

 in trapping for the indigenous rats of the country. In the Province of 

 Chiriqui, Panama, Mr. J. H. Batty in this way unwittingly collected a 

 very large series of Mus rattus ; but, as already said, hybrids of M. rattus 

 and M. alexandrinus, combining in endless variety the characteristics of 

 both species, are widely dispersed in tropical America. 



The common House Mouse [Miis musculus Linn.), although not repre- 

 sented in the present collection, doubtless also occurs in Patagonia, as it 

 is the most widely dispersed in America of any of the introduced species of 

 Mus. Darwin obtained it on East Falkland Island and at Maldonado. 

 It has found its way to subarctic America, in Alaska and the remote in- 

 terior of northern British Columbia. It is at home, thence southward 

 everywhere, under the widest possible conditions of environment. Almost 

 every collection of small mammals, whether made in the arid regions of 

 our great Southwest, the swampy districts of the Gulf Coast, the hot low- 

 lands of Mexico, Central and South America, or at high altitudes in the 

 Peruvian Andes, contains specimens of this omnipresent pest. It will be 



