464 dr. e. a. goeldi on the [June 5, 



(Hernia rus, Mierodelphys) of most authors, and may say that this 

 species is here almost more frequent than Micoureus pugillits. 



Mr. O. Thomas (I.e. p. 363 et seq.) admits two species of three- 

 lined Peramys — a larger (P. americanus) and a smaller (P. iheringii), 

 giving a good figure of the latter on plate iv. 



The habitat of P. americanus is mentioned as " Brazil " (type not 

 in existence), and that of P. iheringii as "South-Brazil," especially 

 Bio Grande do Sul (type in British Museum). Mr. Thomas 

 says of P. iheringii :■ — " This species appears externally to be 

 merely a dwarf form of P. americanus, but it may always be dis- 

 tinguished not only by its much smaller size, but by the different 

 shape of the skull, and especially by the marked flattening of the 

 frontal region." 



I confess my scepticism about the opinion of Mr. Thomas, and 

 I think I have serious reasons to do so. Concerning the measure- 

 ments this author states that he follows Burmeister, " Erlaut." 

 p. 84, giving the dimensions of the same individual. But Bur- 

 meister writes : — whole length 7" (that is 7 Prussian inches), 

 tail 2" 2'" (2 Prussian inches 2 lines). The Prussian inch is 

 2-6154 cm., and the dimensions are equal therefore to 183 mm. 

 (whole length) and 57*53 mm. (tail), while Mr. Thomas reduces 

 them to 18!) mm. and 59 mm. — a perceptible difference for a small 

 animal. The dimensions of a second individual preserved in the 

 Berlin Museum are said to be 168 mm. (whole length) and 61 mm. 

 (tail). On the other hand, the dimensions of the type specimen 

 of P. iheringii (adult?) described by Mr. Thomas are 110 mm. 

 (whole length) and 43 mm. (tail). So long as the minimum size 

 of P. americanus and the maximum size of P. iheringii are not exactly 

 determined by large series of authentic adult specimens, a definite 

 conclusion seems to be a very difficult matter ; and as the question 

 now stands it may be allowed to interpret the difference of size 

 as the expression of different age, the more as the shape of the 

 skull is evidently also affected by growth, as proved by E. Hensel 

 in his memorable investigations. I see that II. Winge shares this 

 opinion, writing: — "P. iheringii, Thomas, synes at stemme ganske 

 med smaa Individer af J/emiurns tristriatus'' 1 ('Pungdyr,' p. 108,) ; 

 and confronting the figures of skulls given by Mr. O. Thomas 

 (Catalogue, pi. xxvii. fig. 8), H. Winge ('Pungdyr,' pi. ii. fig. 9), and 

 Burmeister (' Erlauterungen,' pi. xi. fig. 7), I am unable to find 

 any other essential character to warrant the admission of two 

 different species. 



1 have had occasion to examine dozens of three-striped Opossums 

 of all ages, and I can assert the existence of variations in colour and 

 size. As regai'ds the colour, young individuals are frequently 

 seen with a yellowish or greyish tinge and exceedingly well-defined 

 and conspicuous black stripes, just as in figure 2 of plate iv. of 

 the Catalogue of Marsupials in the British Museum. Older indi- 

 viduals, generally more rufous, often show only pale stripes, and, 

 not rarely, specimens will be met with apparently stripeless, the 

 stripes only appearing against the light. 1 frankly confess that 1 



