SOUTH AMERICA 377 



Order RODENTIA: Gnawing Mammals 



The rodents, as an order, are discussed hereinbefore (p. 41). 

 Representatives of four family groups in South America are 

 considered vanishing forms: 



(1) Cricetidae. The rats and mice of the New World are 

 separated from most of the Old World types by important 

 dental characters, although frequently similar in appearance. 

 Six species of two genera of rice rats, peculiar to the Galapagos 

 Islands, are in danger of extinction. 



(2) Myocastoridae, hystricoid water rats, or coypus. Three 

 races are in need of protection because of persecution for their 

 fur. 



(3) Dinomyidae, hystricoid giant rats. A single species is 

 considered here. 



(4) Chinchillidae. Three races of the rare chinchilla are in 

 need of protection. J. E. H. 



Family CRICETIDAE: Hamsterlike Rodents 

 THE GALAPAGOS RICE RATS 



The Galapagos group of islands, lying on the Equator nearly 

 600 miles due west of the western coast of Ecuador, is remark- 

 able for the various peculiar endemic birds found there, in- 

 cluding the flightless cormorant, the dwarf penguin, and such 

 land birds as Geospiza, while among reptiles there are sundry 

 species of giant land tortoises, large iguanas of a genus peculiar 

 to the islands, and others. The land mammals, however, until 

 a few years ago were believed to comprise but two species 

 related to the continental rice rats of the genus Oryzomys. 

 Later explorations have now raised the number of indigenous 

 rodents to six, representing two related genera, Oryzomys and 

 Nesoryzomys. Commenting on these discoveries, Osgood 

 (1929) writes that the native rodents now "take on consider- 

 ably more importance than formerly and will doubtless need 

 serious consideration in speculation regarding the derivation 

 of the insular fauna. Until thorough study of mainland forms 

 is made, however, no satisfactory conclusions are to be ex- 

 pected. While the oryzomyine rodents are widely distributed 

 and greatly varied in South America, they are also highly 

 developed in Central America, and no competent study of the 



