MAMMALIA. 



49 



inner side are yellow at the apex and gray at the base ; on the outer side 

 they are of a brownish colour, and on the fore part blackish. The hairs of 

 the moustaches are short and slender, and of a brownish colour. The head 

 is large. 



Length from nose to root of tail 

 of tail 

 from nose to ear 



Lines. 

 3 

 9 

 



Length of tarsus (claws included) 

 of ear 



In. Lines. 

 10 

 4A 



Habitat, Maldonado, La Plata, {June.) 



This species is rather larger than the common mouse ; its head is proportion- 

 ately larger, the ears are smaller, the tail considerably shorter, and the fur longer, 

 and in colouring it is a little darker. In size and colour it resembles M. Magella- 

 nicus, but the shorter tail and tarsi, and the smaller size of the ears will serve to 

 distinguish it. 



The skull of Mus arenicola, Plate 34. fig. 7, a, is rather larger than that of 

 Mus Musculus, the nasal portion is broader, the interparietal bone is much 

 smaller, especially in antero-posterior extent ; the zygomatic arches are more 

 slender, and the incisive foramina are broader. The horizontal ramus of the lower 

 jaw (PI. 34. fig. 7, d.) is rather less curved, the coronoid process is more elongated, 

 and the condyloid is narrower and also larger. The length of the skull is 11 lines 

 and a half; the width is 6J- lines. The molars of the upper jaw are figured in 

 plate 34 fig. 7, b. and those of the under jaw, fig. 7, c. 



" This specimen was caught on the open grassy plain, by a trap baited with 

 a piece of bird ; it is, however, very abundant in the sand hillocks near the coast 

 of the Plata. "— D. 



1 3. MUS BRACHIOTIS. 



Plate XIV. 



Mus brachiotis, Waterh., Proceedings of the Zoological Society of London for February 1837, p. 17. 



M. supra obscure^ fuscus, subtus obscure griseo tinctus ; pedibus griseo-J'uscis ; 

 auribus parvulis ; caudd quoad longitudinem, corpus fore cequante : vellere longo 

 et molli. 



Description. — Fur soft, very long, and dense ; ears very small ; general colour 

 brown : the hairs of the upper parts, and sides of the head and body are of 



H 



