496 j\Ir. O. Thomas on some 



Hob. Source, Island of Maraj6, Mouth of the Amazon. 



Type. B.M. 97. 4. 1. 2. 



This little vat is interesting on account of its small size, 

 for with the essential characteristics (and among other tilings 

 the proportionally large feet) of the big rats of the genus Hoh- 

 chilus, it is no larger than middle-sized Oryzomys, such as 

 0. laticeps. 



In working out this species I find I have hitherto been 

 wrong in uniting Nectoviys, Peters * with HolochiluSy and 

 now think they should both stand as genera. Winge united 

 Eolochilus with Sigmodon, but among other things tiie larger 

 and much more complicated posterior upper molars of Holo- 

 chihs and the differences in the character of the feet will 

 readily separate the two. 



So far as is yet known, the genus Holochilus is confined to 

 the eastern half of S. America, from Marajo, where the 

 smallest species occurs, southwards to Bahia Blanca, where 

 Darwin obtained the largest one, figured and described by 

 Waterhouse f as Mus brazili'ensis, but which ought, I believe, 

 to be distinguished from that animal, and might therefore 

 bear the name of IJ. Darwt'ni. On the Parana and Uruguay 

 systems down to La Plata there occurs a white-bellied form 

 to which one or both of the names //. viJpinus, Bts., and //. 

 caneUinus, Wagn., may a])ply. This is found at least as far 

 inland as Goya, Corrientes, whence Mr. R. Perrens sent 

 several examples. //. sciureus, Wagn., from the San Fran- 

 cisco R., is intermediate in size as in locality between these 

 larger southern species and the little //. nanus. Two names, 

 //. brasiliensis, Geoffr., and //. leucogaster, Brandt, I have 

 not as yet been able to identify with certainty. Possibly 

 both apply to the intermediate form I have provisionally 

 called i/. sciureus. 



Akodon fuscinuSy sp. n. 



Nearly allied to A. lasturus, Lund, but smaller, and with 

 more of the general appearance of the species of the olivaceus 

 group. 



Fur straight and close, not woolly, some 10 millim. in 

 length on the back. General colour coarsely lined black and 

 dark yellowish, the resulting colour being a dark grizzled 



« In founding Kecfomt/s (\hh. Ak. Rerl. 1H60, p. 151), Peters inci- 

 dentally speaks of " Holochihyntjs {Holochilm, Waffn. nee Brandt) "; but 

 Warmer's Holochilus, Scbr. Siiiig. Suppl. iii. p. 184.'i, is unquestionably 

 identical with Brandt's, as the description of the teeth and the speciea 

 included clearly prove. 



t Zool. Voy." ' Bengle,' Mamm. p. 58, pi. xix. (1840). 



