io FIELD MUSEUM or NATURAL HISTORY ZOOLOGY, VOL. XIV. 



displayed by the two families may be explained by convergence. Un- 

 til the upper dentition, skull and feet of the Casnolestidae, and espe- 

 cially of the primitive members of the family, are fully known, this must 

 remain an unsettled question. At present the arguments in favor of the 

 alternatives expressed are about equally balanced." 



The next author to give special attention to Ccsnolestes was Miss 

 Pauline Dederer (1909), who made a study of the skull and pointed out 

 certain resemblances to polyprotodonts, concluding that "While there 

 is undeniably a series of forms connecting C&nolestes with the Diproto- 

 donts in tooth structure, yet C&nolestes itself is so generalized in this 

 respect that we may perhaps, in the absence of corroborating characters, 

 question its inclusion within this group. Possibly it may be found to be 

 an offshoot from the Polyprotodonts, as it appears structurally to be 

 more generalized than any Diprotodont, and therefore it might well 

 occupy a separate suborder, as Thomas suggested the Paucituberculata 

 of Ameghino." 



Gregory (1910, p. 211) refers to Miss Dederer's work and concludes 

 that "the detailed characters of the skull show no striking Diprotodont 

 characters and the writer is inclined to regard Canokstes and its allies 

 as an independent suborder, an offshoot of primitive Polyprotodonts, 

 which has paralleled Diprotodonts in certain characters of the denti- 

 tion." Accordingly he places Ccenokstes in the suborder Paucituber- 

 culata with the parenthetical suggestion that the group might be called 

 the Casnolestoidea. Gregory also discusses the possible relationship of 

 the csenolestids to Propolymastodon and allied forms regarded as 

 multituberculates by Ameghino. He concludes his treatment of the 

 marsupial group by stating that "The problem of the genetic relations 

 of the Diprotodontia and the Polyprotodontia is complicated to a cer- 

 tain extent by the existence of the Csenolestoids; but the opinion may be 

 expressed that probably the resemblance of certain Casnolestoids to the 

 Multituberculates is an instance of convergence between related sub- 

 orders, and that the same is true, but to a less extent, of the resem- 

 blances of other Caenolestoids to the Diprotodont phalangers." Sub- 

 sequently (Osborn, 1910, pp. 515-518) the classification proposed by 

 Gregory was somewhat modified and the caenolestids were included in 

 the suborder Diprotodontia as a superfamily, the Caenolestoidea. 



Broom (1912), in his special paper "On the Affinities of Casnolestes," 

 reviewed the evidence adduced by Miss Dederer and pointed out cer- 

 tain resemblances to polyprotodonts not previously noted. He concluded 

 that " as Ccenolestes differs from the typical Polyprotodonts only in 

 tooth specialization, it should not be removed from the Polyprotodontia, 

 but merely be made the type of a distinct family, or section at most." 



