378 EXTINCT AND VANISHING MAMMALS 



whole group has yet been undertaken. When such a study is 

 made, it may be possible to determine something more than 

 the general affinity of the insular and continental forms. At 

 present, it can not be affirmed even that the nominal genus 

 Nesoryzomys is confined to the Galapagos, for at least in some 

 of its characters it is closely paralleled by certain forms of the 

 mainland. However, the number and diversity of the island 

 rodents may perhaps be taken as indicating that their existence 

 on the islands is not an accidental matter and the view is 

 somewhat substantiated that the present land area has been 

 reduced from former larger proportions. Furthermore, it 

 seems quite certain that before the introduction of house rats 

 the native rodents were more generally distributed throughout 

 the different islands of the group than at present." Since the 

 various species have much general similarity in appearance, they 

 may have been frequently confused with house rats by casual 

 visitors, and so neglected with the result that very little is as 

 yet known of them. The six species hitherto described are the 

 following: 



CHATHAM ISLAND RICE RAT 



ORYZOMYS GALAPAGOENSIS (Water-house) 



Mus galapagoensis Waterhouse, Zool. Voyage of the Beagle, Mammalia, pt. 2, p. 65, 



1839 ("Chatham Island," Galapagos group). 

 FIGS.: Waterhouse, 1839, pi. 24 (animal in color), pi. 33, fig. 8, a-c (skull and teeth), 



pi. 34, fig. 14, a (lower jaw). 



Slightly smaller and more delicately built than a roof rat, 

 this species has rather large thin ears, a tail about as long as the 

 body, and in color is brownish above, with a mixture of black 

 hairs and others having a subterminal yellowish band; the sides 

 are yellowish, and the under surface of the body is whitish, with 

 a faint yellowish wash and with dark gray bases to the hairs. 

 Feet whitish; tail distinctly bicolor, dark above, white below. 

 Head and body about 6 inches long (150 mm.) ; tail, 4.75 inches 

 (120 mm.); hind foot, iVe inches (about 30 mm.); length of 

 skull, 31 mm. 



The colors and general appearance of many of the small 

 rodents of South America are rather nondistinctive, so that 

 cranial characters give the best clues to the genera. Oryzomys 

 is characterized by the double series of enamel tubercles on 

 the anterior molars, with narrow secondary enamel folds 

 between them. 



