ORDER MARSUPIALIA. 1 277 



forms characterised by the small size of the talon of the lower 

 molars ; while the names Dicrocynodon (Diplocynodon)^ Docodo?i, 

 and Emieodon * have been applied to more or less closely allied 

 forms from the same deposits. Finally, Professor Osborn has 

 given the name Kurtodon to certain upper jaws from the English 

 Purbeck, which are probably referable to one or other of the above- 

 mentioned genera. From the Laramie Cretaceous of North America 

 Professor Marsh has described the remains of allied types. One of 

 these has been termed Didelphops (Didelophodon or Cimo/estes), while 

 one tooth has been referred to the Jurassic genus Dryolestes, and 

 another has been made the type of the genus Pediomys. The re- 

 semblance in the structure of the lower molars of the Amp hither iince 

 to that of the corresponding teeth of Dasyurus and the Didelphyidce, 

 suggests that the latter have originated from an allied stock. 



Family Spalacotheriid^e. — The genus Spalacotherium, with 

 which Peralestes is identical, has a dentition which may probably 



be expressed by the formula I. -, C. -, Pm. , M. -. The 



3 1 46 



true molars consist of a single column carrying three cusps, and 

 thus corresponding to the blade of the tooth of the Amphitheriince. 

 The reduction in the number of the lower incisors distinguishes 

 this family from the last ; but it is difficult to say whether the 

 absence of the talon in the lower true molars is or is not a more 

 specialised feature. The molars, which are of the typical trituber- 

 cular type, approximate very closely in their plan of structure to 

 those of the genus Chrysochloris among the Insectivora, but this 

 cannot be taken as indicative that the present genus should be 

 referred to that order, since a precisely analogous resemblance ex- 

 ists between the molars of Tupaia in the Insectivora and Perameles 

 in the Marsupials. Menacodon, from the Upper Jurassic of North 

 America, is an allied genus. 



Family Triconodontid^:. — The last family of Mesozoic Mam- 

 mals we have to consider is represented by the English Purbeck 

 genus Triconodon (Triacanthodon), and the allied or identical 

 Priacodon (fig. 1147) of the Upper Jurassic of North America. 

 Professor Osborn includes in this family the Phascolotheriince 

 already mentioned ; but the reduction in the number of the in- 

 cisors and the general fades of the teeth seems to indicate con- 

 siderable difference — although the two groups are probably more 

 or less nearly related. The mandibular condyle is placed still 

 lower than in Phascolotherium, and apparently, indeed, than in 

 any other known Mammal. The upper cheek-teeth resemble the 

 lower. The dental formula in the mandible is I. 3, C. 1, Pm. 4, 

 M. (3-4). The incisors were approximated, the cheek-teeth have 

 1 Preoccupied, see page 1015. 



