RODENTIA 291 



what resembling our own northern muskrat." At the spring auction 

 sales in 1920, 150,000 were sold in St. Louis, 58,000 in New York 

 and 20,500 in London, at from 50 cents to $6.10 each. 64 Formerly 

 about 6,000,000 pelts were received annually, and were used mostly in 

 the manufacture of felt hats, but in 1900 the catch had dropped to 

 1,500,000, worth $444,000 at prices then prevailing. 65 In the 3-year 

 period, 1919-1921, the reported sales totalled only 1,941, 784,^ or an 

 average of 647,261 per annum. 



One group of South American rats has received the generic name 

 Ichthyomys, because of their pronounced fish-eating habit. 67 



FAMILY MURIDAE OLD WORLD MICE AND RATS 



The European house mice (Mus muscidus), introduced into the 

 United States and other American countries, seldom do much damage 

 to field crops, as they are found chiefly about buildings ; but they de- 

 stroy large quantities of stored grain and provisions, damaging as much 

 as they destroy, because they run about in all sorts of places and track 

 filth over exposed food supplies. 1 However, there has been one serious 

 outdoor plague of these little pests, when they became very destructive 

 to crops and forage in a California valley. This outbreak is discussed 

 on a preceding page, in the introductory remarks on rodents. The total 

 amount of damage done by them annually in the United States doubt- 

 less runs up into millions of dollars, but is difficult to estimate with 

 accuracy. There is an account of one house mouse in captivity killing 

 and eating lizards placed in the cage. 2 



The European brown rats, or house rats (Rattus norvegicus, better 

 known as Mus norvegicus), also transported into nearly all parts of 

 the civilized world, are a scourge to the human race. As with the house 

 mouse, they congregate about buildings and grain stacks and do an 

 immense amount of damage, estimated at $200,000,000 per annum. 3 



With the lapse of ages the rat has become a parasite on man. It has developed 

 into the greatest rodent pest ever known. It is far more destructive, directly 



**Laut, The fur trade of America, pp. 120, 123, 1921; Concerning beaver and 

 nutria, Forest and Stream, LXIX, 57, 88, 89, 1921. 



M Stevenson, Utilization of the skins of aquatic animals, Kept. U. S. Fish Comm. 

 for 1902, pp. 283, 317. 



66 Osborn and Anthony, Journ. Mammalogy, in, 226, 1922 ; Natural History, xxn, 

 393, 1922. 



61 Thomas, On a new fish-eating rat from Bogata, Ann. and Mag. Nat. Hist., Ser. 

 9, viii, 164-165, 1924; A new fish-eating rat from Equador, ibid., 541-542. 



1 Howell, N. Amer. Fauna, No. 45, p. 59, 1921. 



2 Burt, A note on the mouse as an enemy to lizards, Copeia, No. 162, pp. 15-16, 

 1927. 



3 Science, LXIX, 378, 1929. 



