116 ^ Mr. 0. Thomas on some 



ventral hairs, but how far this is in part a character of age 

 Teinains to be seen. 



Tlie present form seems most nearly allied to G. chaco- 

 ensis and lockicoodi, but for the moment I prefer not to 

 veiiture a definite determination of it. Its teeth and bullae 

 are larger than in the geographically adjacent G. centralis. 



4. Phyllotis sp. 



S. 224, 227. 234, 235, 239, 240, 246, 249, 258,269, 271, 

 272, 283, 286, 287, 290 ; S. 238, 243, 255, 270, 276, 277. 



Apparently not distinguishable from Ph. loolffsohni, Thos., 

 but the members of the darwini 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 Ph. daricini in this respect. Well- 

 developed supraorbital ridges are characteristic of Oraomys. 



As in other places the Fhyllotis 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 are more or less drabby or brownish. 



5. Oryzomys flavescens, Waterh. 



? . 241. 



liather larger than Uruguay examples. 



6. Akodon glaucinus, sp. n. 



J . 222, 225, 242, 259, 2^&, 268, 280 ; ? . 229, 230, 267. 



Externally closely similar to the Tucuman A. simulatory 

 but the general colour is paler and less '' saturate," the bufl[y 

 or clay-colour of the dorsal area is less intense and is absent 

 or scarcely perceptible on the crown, while the shoulders and 

 the area behind the ears are distinctly more bluish grey. 

 The w hite patch on the chin is constantly present, as is also 

 probably the case in A. variiis, but, owing to the condition of 

 the skins of the latter, it was not originally perceived. 



Skull apparently similar in shape to that of simulator. 

 Supraorbital edges, even of the oldest specimen, not very 

 sharp.- Set of incisors of the normal orthodont nature, not 

 proodont as in A. lacteris. 



