342 



than in the upper jaw : there are five tubercles on each, four placed in two transverse pairs, 

 the anterior being the highest, and a fifth forming the anterior and internal angle of the 

 tooth : the anterior and external angle seems as if it were vertically cut off. 



The smaller species of Didelphis, which are the most numerous, fulfil in South America 

 the office of the insectivorous Shrews of the old continent. Their external resemblance is so 

 close, that some have been described as species of Sorex, but no true representative of this 

 placental genus has hitherto been discovered in South America. The larger Opossums 

 resemble in their habits, as in their dentition, the carnivorous Dasyures, and prey upon the 

 smaller quadrupeds and birds ; but they have a more omnivorous diet, feeding on reptiles and 

 insects, and even fruit. One large species (D. cancrivora) prowls about the sea-shore, and 

 lives, as its name implies, on crabs and other crustaceous animals. Another species, the 

 Yapock, frequents the fresh waters, and preys almost exclusively on fish. 



Hunterian. 



1869. The skull of a Virginian Opossum (Didelphis Virginiand). Hunterian. 



1870. The separated bones of the head of a young Opossum (Didelphis Virginiand). 



The carotid enters between the basi- and ali-sphenoid, in advance of the hinder end of the 

 latter bone, and opens above at the hinder fourth of the basisphenoid, separated from its 

 fellow by an interval of twice the diameter of the canal, at the sides of the depressed sella 

 turcica. 



Hunterian. 



1871. The axis vertebra of the Virginian Opossum (Didelphis Virginiand). 



It is chiefly remarkable for the thickness as well as height, and antero-posterior extent of 

 the spine, and for the hypapophysial ridge of the centrum. 



Hunterian. 



1872. The third cervical vertebra of the same Opossum. 



The hypapophysial ridge is here also developed, but the vertebra is chiefly remarkable for 

 the thick four-sided column of bone formed by the neural spine. 



Hunterian. 



Genus Peramcles. 



1873. The skeleton of the Perameles or Bandicoot Opossum (Perameles nasutd). 



The anterior dorsal and the lumbar vertebra are remarkable for the length and slenderness 

 of their spinous processes, which incline towards each other. The marsupial bones are long 

 and slender. The inner condyle of the hunierus is perforated. The first and fifth digits of 

 the hand are almost obsolete ; the fourth is short and weak ; the second and third are of 

 equal length ; the third is the strongest. The ungual phalanges are cleft in the foot : the 

 fourth toe is the longest and strongest. The ungual phalanx of this and of the fifth toe are 



