116 Mr. O. Thomas on some 
ventral hairs, but how far this is in part a character of age 
remains to be seen. 
The present form seems most nearly allied to “G. chaco- 
ensis and lockwoodi, but for the moment I prefer not to 
venture a definite determination of it. Its teeth and bullee 
are larger than in the geographically adjacent G. centralis. 
4, Phyllotis sp. 
GO. 224, 227, 234, 235, 239, 240, 246, 249, 258, 269, 271, 
272, 283, 286, 287, 290; ¢. 238, 243, 255, 270, 276, 277. 
Apparently not distinguishable from Ph. wolffsohni, Thos., 
but the members of the darwint group are all so closely 
allied that without a special study of them a definite deter- 
mination is not easy to arrive at. 
The presence of divergent supraorbital edges in the type 
of Ph. wolffsohni, as described in the original account, 
appears to be abnormal, or due to great age, as specimens 
since received are like PA. darwini in this respect. Well- 
developed supraorbital ridges are characteristic of Graomys. 
As in other places the Lhyllotis and Graomys live side by 
side, and are by no means always easy to distinguish from 
one another at first sight. The latter, however, has a longer 
and more hairy tail, and its belly-hairs, whether grey at base 
or not, have always definitely white tips, while those of the 
Phyllotis ave more or less drabby or brownish. 
5. Oryzomys flavescens, Waterh. 
9. 241. 
Rather larger than Uruguay examples. 
6. Akodon glaucinus, sp. n. 
6 . 222, 225, 242, 259, 266, 268, 280; 9. 229, 230, 267. 
Iuxternally closely similar to the Tucuman <A. simulator, 
but the general colour is paler and less “ saturate,” the buffy 
or clay-colour of the dorsal area is less intense and is absent 
or scarcely perceptible on the crown, while the shoulders and 
the aiea behind the ears are distinctly more bluish grey. 
The white patch on the chin is constantly present, as is also 
probably the case in A, varius, but, owing to the condition of 
the skins of the latter, it was not originally perceived. 
Skull apparently similar in shape to that of stmulator. 
Supraorbital edges, even of the oldest specimen, not very 
sharp. Set of incisors of the normal oitledont nature, not 
proodont as in A. dactens. 
