356 Mr. 0. Thomas on some 



Skull : back of interparietal to nasal tip 28*6, greatest 

 breadth 15; nasals 12x3*6; interorbital breadth 5"5 ; inter- 

 parietal 2*7 X (c.) 8 ; length of outer wall of infraorbital 

 foramen 3; palate length from henselion 13*2 ; diastema 7'7; 

 palatine foramina 4*8 x2'l; upper molar series 4*6. Lower 

 jaw : condyle to incisor-tip 185 ; height of ramus below 



sn 4-1. 



Hob. Pallatanga, Ecuador. Coll. L. Fraser. 



Type: B.M. 59.11.1.9. 



This species is based on a specimen marked in Mr. Tomes's 

 handwriting "Hesperornys arvicoloides, Pictet," and is there- 

 fore evidently not his own H. caliginosus, with whose descrip- 

 tion externally it somewhat agrees. There are also, as 

 Mr. Allen has pointed out *, other reasons for thinking 

 II. caliginosus to have been an Acodon, an opinion on which 

 I based my original determination of the specimens in 

 Messrs. Stolzmann and Jelski's collections. 



Pictet's arvicoloides, although withdrawn by its author in 

 favour of Renggeri, Waterh., might have to stand for Bahian 

 examples of the olivaceus group ; but in no case has it any- 

 thing to do with the present species. 



Oryzomys phceopus obscurior, subsp. n. 



Similar to the typical variety in most essential respects, 

 but the feet are shorter and more delicate, and the colour is 

 much darker throughout, especially on the posterior back, 

 where the fur is practically black, only relieved by a few 

 yellow-tipped hairs. Upper surface of hands and feet, and 

 tail, both above and below, brownish black. Fifth hind toe 

 only reaching to the base of the first phalanx of the fourth. 



The muzzle of the skull is even shorter than in the typical 

 form ; but this may be due to the fact that the type of 

 phceopus is a very aged specimen, while that of obscurior is 

 only just adult. 



Dimensions of the type (in skin) : — 



Head and body 111 millim.; tail (imperfect at tip) 89 + ?; 

 hind loot (moistened) 22*4 ; heel to front of last foot-pad 9*5. 



Skull : bregma (back corner of frontals) to nasal tip 19 ; 

 greatest breadth (c.) 15; nasals 10'5x 3'4; interorbital breadth 

 5*9 ; palate length from henselion 12'2 ; diastema 7*4 ; 

 palatine foramina 4'5x 2*1 ; upper molar series 4 # 5. Lower 

 jaw : condyle to incisor-tip 18 ; height of ramus below ^71 3*7. 



Bab. Concordia, Medellin, Colombia. Coll. J. K. Salmon. 



Type: B.M. 73.11.5.5. 



* Bull. Am. Mus. N. H. iii. p. 210 (1891). 



