1906.] ON THE TKETH OF CREODONTS. 45 



3. On the Minute Structure of the Teeth of Creodonts, with 

 especial reference to their suggested resemblance to 

 Marsupials. By Charles S. Tomes, M.A., F.R.S., 

 Vice-Pres.Z.S. 



[Received January 15, 1906.] 



(Text-figures 12-25.) 



That the Creodonts, though obviou^sly not Marsupials, never- 

 theless present resemblances to them has been noted by many 

 observers. Filhol (1) has discussed the question, and Matthew (2) 

 uses the expression " pseudo-marsupial characters of the Mes- 

 onychidte," while he also says of Pachycena that " in its dentition 

 this species approximates the Marsupial dental formula." 

 Lydekker (3) goes a little further, and says " these and other 

 fossil forms, such as Borhycena, seem to indicate an intimate 

 relationship between the Polypi'otodont Marsupials and the 

 Creodont Carnivores represented by HycBnodonr Wortman (4) 

 also speaks explicitly upon the same point; whilst frequently 

 alluding to marsupial resemblances in their osteology and den- 

 titions, he says : " By taking the more primitive members of the 

 existing marsupials as the basis of our comparisons, I am 

 convinced we shall be able to arrive at a very much clearer 

 understanding of wha.t the ancestors of the Creodonts were like " ; 

 and " Present evidence points to the fact that the two groups of 

 the Creodonts probably arose side by side from Mesozoic Marsu- 

 pials," and further " that they were derivatives or offshoots of 

 any pre-existing group of Placentals is exceedingly unlikely." 



Such speculations being rife, it occurred to me that it would be 

 interesting to ascertain what evidences of affinity the minute 

 structure of their teeth might afford, and by the kindness of 

 Dr. Matthew, of the American Museum of Natural History, 

 I have been enabled to make sections of the teeth of a number of 

 representative species of Creodonts, whilst Dr. Smith Woodward 

 has kindly furnished me with a fragment of a premolar of 

 Borhycena. 



But, before detailing the results of an examination of these 

 teeth, it seems desirable to say a few words upon the nature and 

 value of the evidence to be derived from the histological structure 

 of teeth, the more so because this line of investigation has been 

 but partially pursued and its results appear to be not well known 

 to the majority of naturalists. 



It might have been expected that there would be but little 

 variety of structure in the teeth of animals belonging to the same 

 great groups, for it is not easy to see how this should be affected 

 by the ordinary processes of selection. It might have been 

 thought that so long as a tooth was strong enough, sharp enough, 

 and well adapted in external form to its work, its structure would. 



