270 3Ir. 0. Thomas on 



Hob. El Saibal, ^X . Cundiuamarca. Cull. G. D. Child, 

 Dec. 22, 1895. 



Ti/pe B.M. no. 98. 7. 3. 4. 



This species is evidently the mainland representative of 

 the insular Z. brevicauda, but is so ditlerent in colour as to 

 require specific separation. 



1 use provisionally Dr. Allen's generic i^xxa ZygodontomySj 

 as these short-tailed rats allied to Oryzomys seem to form a 

 natural group, and there is a convenience in their having a 

 special name. At the same time the dental character which 

 he states to be peculiar to them, and on which he bases the 

 name (the presence of a longitudinal ridge connecting the 

 pairs of cusps), appears to occur in all Oryzomys, including 

 the typical species 0. j^a^ustris, Harl. But Zyyodontomys 

 (as represented by Z. brevicauda and Z. brunneus) has a 

 distinguishing character in the absetice of the transverse ridge 

 running outwards from the longitudinal yoke between the 

 pairs of cusps, and the consequent unusual simplicity of the 

 molars*. The absence of this transverse crest, wliich some- 

 what fills up the valley between the laminae, tends to make 

 the longitudinal yoke much more prominent in Zyyodontomys, 

 and therefore no doubt accounts for the stress which 

 Dr. Allen lays on the latter crest. 



The species described by myself as Oryzomys 7nicroiiniiii '\ 

 from Surinam will also fall into Zyyodontomys. 



PhyUotis Haygardi, sp. n. 



Very similar to Ph. Darwini in colour and other essential 

 respects, but much smaller, and with the ears oidy about half 

 as large. 



Fur about 11 millim. long on the back. General colour 

 soft fawny grey, liberally mixed with blackish on the back. 

 Sides clearer fawn, especially where edging the white of the 

 belly. Under surface white, not sharply defined, the grey 

 bases of the hairs showing through. Ears large, but not of 

 abnormal proportions, both their surfaces well haired, blackish, 

 finely mixed with yellow ; a few bright orange hairs round 

 their anterior base. Eyes without marked orbital rings. 

 Upper surfaces of hands and feet silvery white. Tail little 

 longer than the body without the head, well haired, its upper 

 surface brown or black, its sides and under surface white. 



* Reference to the absence of the transTerse ridge in certain Crice- 

 tina3 has been made by Winge (' Gnavere fra Lagoa Santa,' p. 11) and 

 Major (r. Z. S. 1897, p. 71G). 



t Ann. & Mag. Nat. Hist. (0) xiv. p. 3o8 (1804). 



