]\rant!Osa marniorata a«f? clegans. 159 



separated from all the rest by the wide flat expanse of the 

 Chaco. 



The diflferent races of M. elegans^ from Peru to Southern 

 Chili, are all fairly uniform in size (head and body 80-100 

 roillim. ; tail 95-120; hind foot 14-16), though some of the 

 largest specimens of typical elegans may attain as much as 

 137-139 millim., with tails of about the same length. Tlie 

 diagnostic tooth-measurement in opossums, the combined 

 length of the first three molariform teeth, ranges from 4"6 to 

 5 millim. All the forms have a darker dorsal area, ex- 

 tending forward to a point between the eyes, a paler lateral 

 band separating the dorsal area from the belly, and interrupted 

 by darker patches on the shoulders and hips, and whitish or 

 pale yellowish bellies more or less mixed, according to the 

 subspecies, with slaty grey. 



The following are the races I should be disposed to recog- 

 nize, with their distribution and diagnostic characters ; but it 

 should be remembered that the colour-differences, though 

 instantly recognizable by eye, are by no means easy to 

 describe. 



1. Marmosa elegans venusia, subsp. n. 



Dorsal area rich and fairly dark, most approaching Ridg- 

 way's " wood-brown." Light lateral areas well defined. 

 Median frontal line generally distinct. Under surface pale 

 yellowish white, mostly mixed with slaty grey, the hairs on 

 the chin, throat, centre of chest, and occasionally of belly 

 above white to their roots. 



Uab. Peru and Northern Bolivia ; Surco, near Lima 

 (Simons) ; Cochabamba, Paratani, and Sucre, Bolivia 

 [Siinons). 



The Sucre specimens, by their rather paler tone, lead 

 towards 



2. Marmosa elegans pallidior, subsp. n. 



General colour pale, approximately " drab-grey," less con- 

 trasted with the lighter lateral areas. Under surfoce nearly 

 wholly white, the hairs bordering the colour of the flanks 

 alone inconspicuously slate-based. 



Hah. Challapata, Bolivia. A desert- form, probably 

 characteristic of the arid country round and northwards of 

 Lake Poopo. 



3. Afarmosa elegans Cinderella, subsp. n. 



Dorsal area darkest of group, nearest to Pidgway's 



12^- 



