1903.] OF THE PERCY SLADEN EXPEDITION. 239 



Type. Adult male. B.M. No. 3.7,7.71. Original number 1050. 

 Collected 30 July, 1902. 



The difference in the structure of the pterygoid fossfe, perfectly 

 uniform throughout the series, seems to make it necessary to 

 give a special name to the Matto Grosso Water-rat ; but as lower 

 down the same river, in Paraguay, specimens agreeing with the 

 true N. squamipes occur, I only distinguish it as a subspecies. 



It may be noted as a curiosity that a very large proportion of 

 the skulls of JVectomys, even when quite old, have their median 

 interparietal suture open, a characteristic very rare in mammals 

 generally. 



20. Oryzomys laticeps Lund. 



6. 1003, 1007, 1008, 1020, 1052, 1053, 1062. 



$. 1004, 1006, 1010, 1016, 1026, 1049. 



These specimens appear to be certainly identical with those 

 obtained by Mr. E-obert on the Rio Jordao *, S. Minas Geraes, 

 not far from the typical locality of the species. 



21. Neacomys spinosus amcenus, subsp. n. 



J. 1061, 1077, 1188. 



$. 1036, 1051. 



Size averaging slightly larger than in the true Peruvian 

 li. spinosus, and tail rather longer. General characters very 

 much as in that animal, in spite of the great distance between 

 the localities. Fur shorter and thinner than in spinosus, especially 

 on the under surface. Colour above bright ochraceous, liberally 

 lined with black along the back, but the dorsal area nevertheless 

 not nearly so dark as in spinosus. Sides clearer fulvous, the 

 yellowish line along their lower edge not so sharply defined as in 

 spinosus. Belly and inner sides of limbs white, the hairs white 

 to their roots ; line of demarcation not very sharply defined. 

 Face rather greyer than body. Ears uniformly brown. Arms 

 and legs like sides, or rather duller ; hands and feet dull whitish. 



Skull as usual varying a good deal in size and shape, but in a 

 general way that of subsp. amoenus is a little larger than 

 that of spinosus, with more rounded brain-case, less developed 

 supraorbital ridges, and slightly larger palatal foramina, but 

 none of these points can be regarded as really distinctive. 



Dimensions of the type, measured in the flesh : — 



Head and body 90 mm. (extremes 80-90) ; tail 102 (102-112); 

 hind foot (s. u.) 23 (22-24), (c. u.) 24-5 ; ear 16 (14-16). 



SkuU — greatest length 24-6 mm.; basilar length 18*1; zygomatic 

 breadth 12-7; interorbital breadth 4*3; palatal foramina 4; 

 length of upper molar series 3'1. 



Type. Old male. B.M. ^Tq, 3.7.7.84. Original number 1077. 

 Collected 11 August, 1902. 



The occurrence of a Xeacomys in this region was quite 



* Of. Ann. Mag;. X. 11. (7) viii. p. 530 (1901). 



