OCT., 1916. MAMMALS, COLLINS-DAY EXPEDITION OSGOOD. 207 



there is tendency for the hairs to have dark bases, the throat, axillae, 

 and inguinal regions being always white to the roots of the hairs. In 

 one old female the entire under parts are pure snowy white sharply 

 separated from the upper parts by a broad (5 mm.) tawny ochraceous 

 lateral line. Both fore and hind feet are more or less brownish, and the 

 ears, while usually tawny, are sometimes dusky antero-internally. 



Two adults present the following flesh measurements: Total length 

 333, 328; head and body 149, 147; tail 184, 181; hind foot 27, 27. 



Hesperomys callosus boliviae Thomas. 



One specimen, Trinidad. 



On geographic grounds, this specimen might be either H. callosus 

 or H. c. bolivice; and with nothing more than descriptions for com- 

 parison, its identification cannot be regarded as positive. The tooth- 

 row measures 4.1 mm., which is exactly the length given for that of the 

 type of H. c. bolivia, and other cranial measurements correspond 

 closely. External measurements are as follows: Total length 200; 

 head and body 122; tail 78; hind foot 23. 



Phyllotis (Graomys) domorum Thomas. 



Three specimens, Parotani. 



These are typical examples of this species and from the region of 

 the type locality. Their examination has been of particular interest in 

 connection with the grouping of certain South American Muridae 

 recently made by Thomas. * A small group including the present species 

 has been given generic rank under the name Graomys, but this group 

 is so closely allied to typical Phyllotis that it seems better to treat it as 

 a subgenus rather than as a genus. This conclusion is largely influenced 

 by a consideration of Phyllotis amicus, a species which is assigned infer- 

 entially by Thomas to Phyllotis but which shows such affinity to 

 Graomys that the exceedingly close relationship between the two 

 groups can scarcely be doubted. In all external features except size 

 the resemblance of P. amicus and P. domorum amounts to practical 

 identity. The very soft, satiny pelage and the pure white self-colored 

 areas of the under parts are very characteristic. The skull of P. 

 amicus has the short, rounded braincase of typical Phyllotis but its very 

 broad frontals and its slightly undercut zygomatic plate show very 

 decided approach to the condition in Graomys. It lacks the definite 

 supraorbital bead but the supraorbital border is trenchant and even 

 slightly elevated. The second upper molar is more nearly five-parted 

 than in true Phyllotis, and in this respect also there is resemblance to 

 *Ann. & Mag. Nat. Hist., (8), XVII, pp. 139-143, Jan., 1916. 



