HISTORY OF THE MARSUPIALIA 



641 



which all the other diprotodonts display so clearly. Dr. 

 Gregory is "inclined to regard Ccenolestes and its allies as an 

 independent suborder, an offshoot of primitive Polyprotodonts 

 which has paralleled the Diprotodonts in certain characters 

 of the dentition." ^ 



Evidently, the animals of this series were extremely rare 

 or absent in the areas where the known South American de- 

 posits of the Pleistocene and 

 Pliocene were laid down, for 

 there is a very long hiatus 

 in their history from the 

 Recent to the Santa Cruz, 

 during which none has yet 

 been found, except one genus 

 ("fZygolestes) in the Parana. 

 In the Santa Cruz, however, 

 there was a great abundance 

 of these little marsupials, to 

 which various generic names 

 have been given and which 

 displayed considerable vari- 

 ety in the forms of the teeth. 

 Some {e.g. \Garzonia) agreed 

 with Ccenolestes in having no 

 trenchant shearing teeth ; 

 behind the large, procumbent lower incisor, followed four or 

 five very minute teeth, which must have been nearly or quite 

 functionless, succeeded by the well-developed molars. Other 

 genera {e.g. jAbderites) had a similar dentition, with the im- 

 portant exception that the last upper premolar and first 

 lower molar were enlarged and trenchant, together forming 

 a shearing pair ; these teeth were vertically fluted or ribbed 

 in very characteristic fashion. The Australian phalangers 



1 W. K. Gregory, The Orders of Mammals ; Bull. Amer. Mus. Nat. History, 

 Vol. XXVII, p. 211. 

 2t 



Fig. 302. — Lower jaws of Santa Cruz cseno- 

 lestid.s, enlarged. A, ]Garzonia patagonica, 

 B, ^Abderites crassignathus. C, ^Callomenus 

 ligatus. (After Sinclair, in Reports Prince- 

 ton University Expeditions to Patagonia, 

 Vol. IV.) 



