380 MARSUPIALS. 



y« SCANSORIA. 



Genus Didelphys, (Opossums). — ^These Marsupials are now exclu- 

 sively confined to the American Continents, although the fossil 

 bones and teeth of a small species attest their former existence 

 in Europe contemporaneously with the PelcBOthere, Anoplothere, and 

 other extinct Pachyderms, whose remains characterize the Eocene 

 strata of the Paris basin. 



The dental formula of the Genus Didelphys (PL 98, fig. 6) is : 



l-I , 3-3 



Incisors — ■ ; canines — ; premolars — ; molars — : = 50. 



4—4 1—1 * r 3_3 ' 4_4 



The Opossums resemble in their dentition the Bandicoots more 

 than the Dasyures ; but they closely resemble the latter in the 

 tuberculous structure of the molars. The two middle incisors of 

 the upper jaw are more produced than the others, from which 

 they are also separated by a short interspace. The canines are 

 w^ell developed ; the upper being always stronger than the lower. 

 The false molars are simply conical, but are more compressed 

 than in the Carnivorous Marsupials. The posterior false molar 

 is the largest in the upper jaw ; the middle one is the largest 

 in the lower jaw : the anterior is the smallest in both jaws. 

 The true molars are beset with sharp cusps which wear down 

 into tubercles as the animal advances in age. The crowns of 

 the upper molars present a triangular horizontal section ; the 

 base of the triangle is turned forward in the posterior molar ; and 

 obliquely inwards and backwards in the rest. In the lower jaw the 

 true molars are narrower and of more equal size 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 oflt". 



The canines still exhibit a superior development in both jaws 

 adapted for the destruction of living prey, but the molars have a con- 

 formation different from that which characterizes the true flesh-feeders, 

 and the Opossums consequently subsist on a mixed diet, or prey upon 

 the lower organized animals. 



