Article I.— ADDITIONAL OBSERVATIONS ON THE 

 CREODONTA. 



By W. D. Matthew. 



Contents. 



I. Classification. Arrangement of the Creodonta, chiefly on 

 the basis of the specialized carnassial. 



II. Family Viverravidae. Characters of the skull and skeleton 

 of Viverravus Marsh (= Didytfiictis Coy>q), as shown in two species, 

 V. protenus and V. leptomylus Cope. 



III. Family Arctocyonidae. Fore and hind feet of Clcenodo?i, 

 with a discussion of its relations to the Ursidae. 



IV. Family Hysenodontidae. Revision of the classification. 

 Revision of the genus Sinopa {Stypolophus) with descriptions of 

 two new forms. 



V. Family Mesonychidse. The oldest known mammal skull 

 {Tritsodon heilprinianus). Dentition and skeleton of Pachytzna 

 gigantea. Pseudo-marsupial characters of the Mesonychidae. 



I. — Classification. 



In classifying any group which includes a large proportion of 

 primitive types we must use some combination of two methods. 

 A division may be considered either as a group of forms resem- 

 bling a given type within certain limits, or as including a particu- 

 lar line of development. Osborn has termed these two principles 

 of classification the " horizontal " and " vertical " ; it appears to 



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