158 Mr. 0. Thomas on 



latter is spotted and banded witli grey and brown on the 

 dorsal side, to harmonize with tlie colouring of the lichen- 

 patched tree-trunks it frequents ; but when attacked it starts 

 into a characteristic attitude of defence, raising its anterior 

 legs and palpi to display the black and yellow slashes of tlieir 

 underside, and stridulates at tlie same time, as a double 

 warning to enemies to keep aloof. 



XXII. — On Marmosa marmota and eleo;ans, with Drscriptions 

 ofneio Suhspecies of the kilter. By Oldfield Thomas. 



Since I wrote my paper on the small Paraguayan ojiossum 

 [Marmosa marmota, or, as it was tlien termed, Micoureus 

 qriseus) * the British Museum has received, firstly, a furtlier 

 consignment of the same interesting animal from Mr. R. 

 Perrens ; secondly, a valuable series of the true .1/. elegans 

 from Valparaiso, collected and presented by Mr. J. A. 

 "VVolfFsohn ; tliirdly, some specimens of the same group from 

 Tucuman (coll. L. Dinelli) ; and, lastly, a number of specimens 

 from Peru and Bolivia collected by the late ]\Ir, Perry O. 

 Simons. These specimens, amounting to about fifty in 

 number, enable me more exactly to trace the characters and 

 distribution of the two forms. 



In 1894 I stated that M. marmota differed from J/, elegans 

 cranially by its more sharply edged supraorbital region, but 

 that externally " the two species were widely different." 



The further material induces me to modify this statement, 

 for fresh specimens show that the two are closely similar 

 externally, and were it not that well-defined supraorbital 

 processes are present in M. marmota and entirely absent in 

 the oldest M. elegans^ I sliould look upon the Paraguayan 

 species as but another local subspecies of the widely-spread 

 Andean form. It may, however, be just distinguished from 

 the most white-bellied of the races of M. elegans by the fact 

 that the under surface, pure white throughout, is sharply 

 defined laterally from the grey colour of the sides, non>e of 

 the lower hairs having any slaty at all at their bases. 



The recognition of M. marmota and M. elegans as species, 

 and the different races of the latter as subspecies, is in agree- 

 ment with their geography, for while all the known localities 

 of M. elegans, far apart as they are, are connected with each 

 other by mountainous country, M. marmota^ in Paraguay, is 



* Ann. & Mag. Nat. Hist. (6) xiv. p. 184 (1894). 



