120 



DE. B. A. BENSLEY ON THE EVOLUTION 



possible to recognize tlie constituent elements. The protocone is either reduced 

 {Oi-yzoryctes) or in the final stages {Ericuliis, Echhiops, Centetes) wholly vestigial or 

 absent. 



E-eferring to the consolidation of the paracone and nietacone in the upper molars, 

 Porsyth Major adds : — " It is only in Notoryctes, which in other respects also is highly 

 specialized and forms a parallel to the Centetidse and still more to the Chrysochloridse, 

 tliat this fusion likewise occurs in all molars ; the protocone in Notoryctes is still 

 developed to a considerably greater extent than in the Centetidaj." 



With reference to the lower molars of the Centetidse, this writer points out that the 

 chief feature is the reduced condition of the taloaid, a character which he believes to 

 be secondary, from the fact tliat this structure is well developed both in the lowest 

 Tertiary and Cretaceous Mammalia. 



Homoplastic consolidation of central cusps of upper molars in Marsupials and Placentals. 

 A. Talpa; B. Poiamogale ; C. Ori/zori/ctes ; D. Perami/s ; E. Notorijctes. (Abbreviations as in text-fig. 4, p. 116.) 



According to this view, the molars of Notoryctes bear the same relation to those of 

 the Dasyuridir, primitive Peramelidte, and Didelphyida3 as those of the Centetidse and 

 especially Oryzoryctes bear to those of the Talpidae. The triangular pillar of the upper 

 molars represents the conjoined paracone and metacone, the large internal cusp a 

 protocone. The external styles, which are virtually three in number, the anterior one 

 being composite, represent «, h, and c of the normal polyprotodonts. The triangular pillar 

 of the lower teeth represents an elongated trigonid, the talonid being vestigial. 



It is apparent that Cope's designation of the molars of Notoryctes as tritubercuJate, 

 although quite applicable to the lower teeth, is misleading as applied to the upper, if by 

 the term " trituberculate " we mean to designate such teeth as those of the Didelphyidte, 

 Talpidfu, and priinitive Creodonta, which present a triangle of three main cusps with or 

 without intermediate conules or external styles. It is further apparent that his view 

 that the minute jn-oportions of the talonid in the lower molars of Notoryctes, Chryso- 

 chloris, and the Centetidse represent a primitive condition, which is prophetic of one 

 in which this structure is well developed, is also erroneous. "While the fact pointed out 



