200 MARSUPIALIA. 



Genus POLYMA.STODON, Cope 1 . 



Syn. Catopsalis, Cope 2 . 

 Tceniolabis, Cope 3 . 



As this is the only genus at present known, its characters are 

 those of the family ; five species have been named. 



Polymastodon tabensis, Cope 4 . 



Syn. Catopsalis poUm; Cope 5 . 

 Taniolabis aulcafus, Cope e . 



This is the type and largest species, its limb-bones being described 

 as equal in size to those of Macropus yiganteus. The mandible and 

 dentition are represented in the accompanying woodcut (fig. 32). 



Hab. North America. 



M. 2568. Part of the left ramus of the mandible, showing the three 

 cheek-teeth in an almost unworn condition ; from the 

 Puerco Eocene of New Mexico, U.S.A. 



Presented by E. LydeJcJcer, Esq., 1885. 



Family TRITYLODONTID^E. 



The upper true molars have three antero-posterior ridges and 

 are elongated transversely ; while the premolars in the type genus 

 are of the same general structure, although somewhat smaller and 

 simpler. It seems probable that Stereognaihus should be included 

 in this family 7 ; but the close resemblance of the molars of the type 

 specimen of that genus to those of Ttitylodon suggests that the 

 specimen in question belongs to the upper rather than to the lower 

 jaw. 



Cope 8 suggests that from the type genus may have been derived 

 both the Polymastodontidce and Plagiaulacida? ; while Thylacoleo 

 is directly descended from the latter, and the Macropodidce and Phas- 

 colomyidce are lateral branches from the same stock. It is, however, 



1 Amer. Nat. vol. xvi. p. 684 (1882). 



2 Ibid. p. 416. This name has the priority, but has apparently been with- 

 drawn by its author in favour of Polymastodon. See Amer. Nat. vol. xviii. p. 688 

 (1884). 



8 Ibid. p. 604. Founded on an incisor ; see Amer. Nat. yol. xix. p. 493 (1885) 

 Ibid. p. 684. Ibid. p. 685. 



6 Ibid. p. 604. Subsequently quoted as T. scalper. 



7 See Cope, Amer. Nat, vol. xviii. p. 688 (1884). Trihjlodon, although the 

 latest in date, is taken as the type of the family on account of the more satisfactory 

 evidence afforded by the type specimen. 



8 Op. tit. p. 605. 



