4 Bulletin American Museum of Natural History. [Vol. XIV, 



so accurate and recent a text-book as Prof. Zittel's, I must dis- 

 claim any really radical changes in relations, except in a few 

 cases. The recent study of far more complete Creodont material 

 than has ever before been accessible has led American students 

 to perceive the fundamental importance of certain lines of ge- 

 netic cleavage somewhat less appreciated hitherto, and to make 

 these the primary basis for division rather than differences which 

 are now perceived to be in large part only contrasts between 

 primitive and specialized types. 



First in importance among these characters of divergent spe- 

 cialization is the position of the carnassial teeth. In the primi- 

 tive types the shear between upper and lower molars is absent 

 or rudimentary and about equally developed on all three molars. 

 In some of the specialized types it is chiefly between p" and m„ 

 as in all modern Carnivora. In others it is chiefly between 

 m' and m^, or between m'' and nij. A large number of the primi- 

 tive genera of the Creodonta show, in some of their species at 

 least, a more or less evident tendency towards one of these three 

 specializations. 



A primary division on these lines, worked out by Dr. Wortman 

 and the writer, and published by Wortman a year ago ('99, p. 

 139), had been previously independently elaborated though not 

 published by Prof. Osborn for use in his University lectures, 

 in either case chiefly the result of study of the large series of 

 Creodonta in the American Museum collections. 



Another line of cleavage as yet imperfectly known, but which 



may prove to be of importance equal to or greater than the above, 



lies in the character of the claw-phalanges. In one group of 



Creodonts they are short, wide, and split, indicating a more or 



less hoof-like claw, probably used for locomotion only. In the 



other they are like those of most modern Carnivores, sharp, 



laterally compressed, bearing apparently a sharp curved claw 



which could be used as a weapon. This character is known in 



the following : 



Clcenodoti (both species) ) 



>• Sharp-clawed. 

 Viverravus (two species) ) 



HycBuodon 



Oxycsna, Patriofelis \ Bhint-clawed. 



Fac/iyana, Mesonyx 



