184 Mr. O. Thomas on Micoureus griseus. 



Mr. Blandford having now published descriptions of the 

 Japanese Platypi, I am able to give the names of the Japanese 

 Histerids I found in their bores : — Tryponceus fcigi, Lew., was 

 feeding on Platypus Severini, Bland., and T. venator, Lew., 

 on P. calamus, Bland. 



XXVI. — On Micoureus * griseus, Desm., with the Description 

 of a new Genus and Species o/'Didelphyidce. By Oldfield 

 Thomas. 



In 1888 1, following the lead of previous writers, and, like 

 them, without Paraguayan specimens for comparison, I iden- 

 tified Azara's " Micoure* a queue longue " J, on which 

 Desmarest's Didelphys grisea, was based §, with the grey 

 opossum of Minas Geraes and Bio Janeiro. This latter was 

 named by Lund in 1841 D. incana ||, a designation which, 

 following the above identification, was naturally placed by 

 rne as a synonym of D. grisea. 



In his work on Minas Geraes opossums Dr. Winge % 

 accepted my identification with a note of warning as to its 

 having been based merely on Rio Janeiran and not Para- 

 guayan specimens, and this warning proves to have been fully 

 justified, for the British Museum has now received the skin 

 of an opossum from Corrientes which, while obviously 

 distinct from the Minas Geraes form, agrees far better with 

 Azara's description than the latter does. 



The specimen was presented by Mr. Thomas Perrens, and 

 was collected by his brother Richard near Goya, on the 

 Parana. The following is a description of it : — 



* The subgenera of Didelphys admitted in the ' Catalogue of Mar- 

 supials ' having been since used by several writers of eminence as full 

 genera, it seems better, as they are unquestionably perfectly natural 

 groups and no principle is involved, to sink my own opinion on the sub- 

 ject and to accept them as such. This course I have also adopted in the 

 case of the groups of Cricetinas, of which the majority of the American 

 members were at one time joined, by American and European naturalists 

 alike, into one genus " Hesperomys. 1 ' If so joined, I still think, as 

 formerly (P. Z. S. 1888, p. 133), that they should also be joined to 

 Cricetus ; but, split apart as they now are, they would all equally retain 

 their own names, while Cricetus would again be used for Old- World 

 forms only. 



t Cat. Mars. B. M. p. 349. 



X Quadr. Parag. i. p. 290 (1801). 



§ Diet. Sci. Nat. xlvii. p. 393 (1827). 



|| Blik. Bras. Dyrev. Dansk. Afh. viii. p. 237. 



IJ ' Jordfundne og nulevende Pungdyr fra Lagoa Santa,' p. 107 ; E Mus. 

 Lundii, 1893. 



