Zoological Society. 125 



tirely deficient in the Chcerojms, unless some rudiments should exist 

 beneath the skin ; at all events only two toes are apparent extern- 

 ally, but they are so armed and developed as to be serviceable for 

 burrowing or progression. The inner toe is wanting on the hind 

 foot. Dental formulae 



Incisors^; canines ~; prsemolares ^ ; molares*-^*: =46. 



All the teeth are of small size ; the canines resemble the spurious 



molares in size and shape, and these are separated at intervals as 



in Myrmecobius. The marsupium opens downwards in the Chceropus, 



as in the true Bandicoots. The species described has no tail. The 



genus would seem by its dentition to rank between Myrmecobius and 



Perameles. Its digital characters are anomalous and unique among 



the Marsupialia. 



Scansoria. 



Didelphidce, Opossums. 



These Marsupials are now exclusively confined to the American 

 Continents, although the fossil remains of a small species attest the 

 former existence of the genus Didelphis in Europe contemporaneously 

 with the Palaeothere, Anoplothere, and other extinct Pachyderms 

 whose fossil remains characterize the Eocene strata of the Paris 

 Basin. The dental formula of the genus Didelphis is, 

 Incisors 5 ~ ; canines ^ ; praemolares|^| ; molares ^ : = 50. 



The Opossums resemble in their dentition the Bandicoots more 

 than the Dasyures, except in the structure of the molares. 



The two middle incisors of the upper jaw are more produced than 

 the others, from which they are separated by a short interspace. 

 The canines are well developed, the upper being always stronger 

 than the lower. The false molares are simply conical ; the true 

 ones beset with sharp points, which wear down into tubercles as the 

 animal advances in as"e. 



In the type of the subgenus Cheironectes, besides being web- 

 footed, the anterior extremities present an unusual development 

 of the pisiform bone, which supports a fold of the skin, like a 

 sixth digit; it has indeed been described, as such, by M. Tem- 

 minck; this process has not of course any nail. The dentition 

 of the Yapock resembles that of the ordinary Didelphis. All the 

 Opossums have the inner digit of the hind foot converted by its 

 position and development into a thumb, but without a claw. The 

 hinder hand is associated in almost all the species with a scaly 

 prehensile tail. 



In some of the smaller Opossums the subabdominal tegumentary 

 folds merely serve to conceal the nipples, and are not developed into 



