MARSUPIALS 189 



first the publication of Dr. Sinclair's memoir on the Marsupials of the 

 Santa Cruz formation.^ Carefully describing the fine material secured 

 by Hatcher and Peterson, Sinclair was apparently enabled to settle the 

 vexed question whether the "Sparassodonts" of Ameghino, including 

 Borhycena and its allies, were Marsupials or Creodonts. Because these 

 genera were Creodont-like in form of skull and teeth, and because they 

 lacked certain "Marsupial" characteristics, such as epipubic bones and 

 palatal vacuities, it had been supposed that they must be Creodonts, or 

 at least must connect the Creodonts with the Carnivorous Marsupials. 

 But Sinclair's analysis of their characters resulted in a very strong case 

 for the view that the Sparassodonts were true Polyprotodont Marsupials, 

 and widely removed from the Creodonts. 



A single outstanding difficulty, however, has led Lydekker in his Ency- 

 clopaedia Britannica articles to reject Sinclair's conclusions and to return 

 to the view that the Sparassodonts are Creodonts. While Dr. Sinclair's 

 memoir was in press, Mr. C. S. Tomes published in the Proceedings of 

 the Zoological Society^ an important article, in which he showed that in 

 the histological structure of the enamel Borhycena differed quite radically 

 from the Carnivorous Marsupials, and agreed with the Inadaptive Creo- 

 donts and the modern Fissipedia; that is to say. Tomes found that in 

 the single premolar of Borhycena available for examination there were no 

 dentine tubules in the enamel, unlike other Marsupials, and the enamel 

 prisms were gathered together into bundles which were twisted and inter- 

 laced in a manner recalling the frayed out strands of a rope — an arrange- 

 ment precisely similar to that in the Inadaptive Creodonts and modern 

 Carnivores, but not found in the Adaptive Creodont Didymictis or in 

 the Oligocene Cynoid Cynodictis. Matthew,^^ in analyzing these results, 

 held that this was merely another character in which Borhycena had 

 progressed beyond the other Carnivorous ^larsupials in paralleling the 

 Placental Carnivores, and that this and other resemblances to the latter 

 groups were of far less weight than the many true marsupial characters 

 noted by Sinclair. 



It is greatly to be desired that Mr. Tomes's investigations should be 

 extended to include the histological structure of the enamel in the less 

 specialized Sparassodonts Cladosictis and its allies, as well as in fossil and 

 recent Didelphids and other groups of mammals. In the meanwhile the 

 reviewer can not help feeling that Sinclair and ^latthew are entirely 

 right in referring the Sparassodonts to the Marsupialia. 



* Rept. Princeton Tniv. Exped. to Patagonia, vol. iv. pt. iii, lOOG. 



» 1906, vol. i. pp. 45-58. 



w Geological Magazine, n. s. (IV), vol. iv, 1907, pp. 531-535. 



