144 Dr. W. T. Caiman on the 



the hairs slaty, with pale bufFy tips. Crown of head like 

 back. Dark orbital rings broad, strongly marked, extending 

 forwards on to the sides of the muzzle. Cheeks and chin 

 clearer buffy. Outer sides of arms and legs like back, inner 

 sides like belly ; hands and feet practically naked, pale 

 brownish. Tail furry at its base for a shorter distance than 

 usual, the fur, which is coloured like that of the back, ex- 

 tending for only about an inch and being surpassed posteriorly 

 by the outstretched feet ; remainder of tail naked, as usual, 

 but instead of being white terminally it is uniformly pale 

 brown to the end, at least above, the under surface being in 

 one specimen slightly paler terminally. 



Skull with well-expanded zygomata and broad interorbital 

 region, with overhanging postorbital ledges. Teeth large, 

 of the usual proportions in this group. 



Dimensions of the type (measured in skin) : — 



Head and body 187 mm. ; tail 245 ; hind foot (s. u.) 23 ; 

 ear 19. 



Skull : basal length 39*5 ; greatest breadth 25 ; nasals 

 18*5 X 6"2 ; interorbital breadth 7*6 ; breadth across post- 

 orbital processes 9"4 ; breadth of brain-case 15; palate 

 lenoth 23*5 ; combined length of three anterior molariform 

 teetti 7-7. 



Rob. Sarayacu, Oriente of Ecuador, 



Type. Female (young adult). B.M. no. 80. 5. 6. 77. 

 Collected by Mr. Clarence Buckley. An old male also in 

 collection. 



This opossum shares with M. regina * alone of the ])resent 

 group the distinction of having a wholly brown tail, not 

 turning to white at its end. From that species it is separated 

 by its duller and less yellowish belly-colour, broader skull, 

 and larger molars. 



XVIII. — On the Classification of the Crustacea Malacostraca. 

 By W. T. Calman, D.Sc. 



In the course of preparing a general account of the Crustacea 

 for a forthcoming volume of Prof. E. Ray Lankester's 

 ' Treatise on Zoology ' I have been led to discard the com- 

 monly accepted classification of the Malacostraca and to 

 adopt a scheme which was briefly outlined by Dr. H. J. 

 Hansen some ten years ago. The object of the present 

 * Ann. k Mag. Nat. Hist. (7) ii. p. 275 (1898). 



