144 Wortman — Studies of Eocene Mammalia in the 



ravidse are distinguished not only by the possession of the 

 primitive characters above enumerated, but by two very 

 trenchant dental peculiarities which the mustelines exhibit, 

 viz. : the great antero-posterior enlargement of the internal 

 portions of the crowns of the superior molars, and the absence 

 of the deep slit-like notch separating the two blades of the 

 superior sectorial. These, together with the absence of the 

 anterior basal cusp on the superior sectorial, the great breadth 

 of the base of the skull, the small rugged bulla,- and long bony 

 spout-like meatus, constitute the real distinguishing features 

 by which the Mustelidse may be separated from the Viverridae. 

 The skeletal characters are otherwise much alike in the two 

 families, the manner of perforation of the transverse process 

 of the atlas being variable in the mustelines. 



With reference to the Felidse, it may be said that our 

 knowledge is not so perfect regarding their origin and Eocene 

 representatives as it is with respect to other living families, so 

 that it is well nigh impossible to make a satisfactory compari- 

 son. If the Palseonictidse are the forerunners of the felines, 

 which seems so exceedingly probable, then the two groups 

 belong to different phyla and may be distinguished by the 

 structure of the superior molars. In the Palseonictidse, it is 

 the posterior part of the crown of the first superior molar 

 which is elongate ; whereas in the Yiverravidse, it is always 

 the anterior part of the crown which is the longer. 



Viverravus Marsh. 



Viverra, a civet cat; and avus, a grandfather. This Journal, August, 1812; 

 Didymictis Cope, Tertiary Vertebrata, 1884; Viverravus Wortman and Matthew, 

 Bull. Amer. Mus. Nat. Hist., 1899, p. 136. 



A group of small or medium-sized civet-like Carnivores, 

 with a number of species distributed throughout the Eocene 

 from the Torrejon to the Bridger inclusive. They are charac- 

 terized by having the dental formula I. f, C. \ , Pm. £, M. f , of 

 which the two superior molars of the dentition have broad 

 tubercular crowns, with great transverse extension of the anterior 

 border, the two external cusps being unequal and placed well 

 inwards from the external margin of the crown ; the second 

 inferior molar, tubercular or becoming so, and much smaller 

 than the first ; the inferior sectorial having a high trigon, with 

 oblique principal shear, a well-developed posterior shear, and 

 a relatively large, more or less basin-shaped heel ; and pre- 

 molars having posterior accessory cusps. 



In his original description of this genus, Professor Marsh 

 says : " A much smaller Carnivore, about the size of the mink, 

 is represented in our collections by two lower jaws with teeth, 

 and a sectorial upper molar of one individual and portions 



