﻿THE OPOSSUMS. 207 



the two colours at their junction. Other characters apparently 

 much the same as in the last species. Length of head and 

 body of male about 12^ inches ; of tail about 15 inches. 



Distribution. — South-eastern Mexico to Paraguay. 



The specimen represented in Plate XXX IV. is the type of 

 Didelphys derbiana, so named from having been originally in 

 the collection of a former Earl of Derby at Knowsley. Mr. 

 Waterhouse, its describer, believed it to represent a distinct 

 species on account of its brilliant coloration, the well-marked 

 white stripe on the withers, and the great relative length of the 

 hairy portion of the tail. The soles of the hind feet are also 

 peculiarly black, while the fore feet are furnished with white 

 hairs, and the naked portion of the tail is clouded with brown. 

 A larger series of specimens have, however, shown that such 

 variations are merely individual and have no specific value. 



This species is one of those in which the young, as soon as 

 they leave the teats, are habitually carried on the back of the 

 mother, with their prehensile tails tightly twisted round her tail. 

 This feature, it may be added, is common to the whole of the 

 small forms constituting the next sub-genus, one of which has 

 a synonym {D. dorsi^^erd) referring to it. 



VII. ASHY OPOSSUM. DIDELPHYS CINEREA. 



Didelphys cinerea, Temminck, Monogr. Mamm., vol. i., p. 46 

 (1827); Thomas, Cat. Marsup. Brit. Mus., p. 342 (1888). 



Micoiireus cinereus, Lesson, Nouv. Table Regne Anim., 

 Mamm., p. 186 (1842). 



Didelphys ?ioctivaga, Tschudi, Fauna Peruana, Mamm., p. 148 



(1844)- 

 Didelphys waterhousei, Tomes, Proc. Zool. Soc, i860, p. 58. 



Characters. — With this species we reach the fourth sub-genus 

 {Micoureus) of the true Opossums, which includes a consider- 

 able number of species, and is characterised as follows : — 



