358 Mr. 0. Thomas on some 



Oryzomys gracilis, sp. n. 



Size small, form very slender and delicate. Fur short and 

 velvety, the hairs of the back only about 4 millim. in length. 

 General colour finely grizzled yellowish brown, perhaps 

 nearest to E-idgway's " raw umber ; " the hair-tips dull 

 yellow, mixed with the blackish longer hairs. Sides clearer 

 and more fawn-coloured, especially along the edge of the white 

 belly-hairs. Whole of under surface white, the bases of the 

 hairs slate, line of demarcation on sides fairly v/qW defined. 

 Ears short, thinly haired, except on the anterior half of their 

 outer surfaces, where they are closely covered with fine shining 

 black hairs, which contrast markedly with the general hue of 

 the upper surface. Uppersides of hands and feet thinly 

 haired, white, probably flesh-coloured in life ; fifth hind toe, 

 without claw, reaching nearly to the middle of the first 

 phalanx of the fourth. Tail slender, thinly haired, brown 

 above and white below proximally, the lower surface darken- 

 ing distally until the terminal fourth of the tail is uniform 

 brown all round. 



Skull with narrow parallel-sided nasals, sharply square 

 supraorbital edges, with a very faint trace of beading. Palatal 

 foramina rounded, open, rather longer than the molar series. 

 Molars narrow, delicate, but distinctly Oryzomys-WkQ in 

 character. 



Dimensions of an adult female skin : — 



Head and body 106 millim.; tail 105; hind foot 24-6; 

 ear 13. 



Skull : tip of nasals to front corner of interparietal 23*6 ; 

 nasals, length 10*4, breadth 2*5 ; interorbital breadth 5 ; length 

 of outer wall of anteorbital foramen 2*5 ; diastema 6'3 ; palatal 

 foramina 4*5 ; length of upper molar series 3'8. Lower jaw : 

 condyle to incisor-tip 15'5 ; height of ramus below ^i 'd'd. 



Bah. Concordia, j\ledellin, Colombia. Coll. J. K. Salmon. 



Type-. B.M. No. 73.11.5.4. 



This species may be readily distinguished from its allies by 

 its graceful form, small black ears, slender feet and tail, and 

 narrow, delicately built nasal region. 



Oryzomys microtinus, sp. n. 



Size rather small ; form more or less Arvicoline. Fur rather 

 short, straight and harsh, the iiairs of the back about 10 millim. 

 in length. General colour coarsely grizzled brown, the hairs 

 dark slate proximally, with dull yellow tips ; many black- 

 tipped hairs intermixed. As a result the colour is not unlike 

 that of some of the darker voles, say Microtus agrestis or 



