424 



PROCEEDINGS OF THE ACADEMY OF 



[1892. 



recent families. In like manner Ampliidozotherium, from the 

 Oligocene, resembles the Ta/puhe in molar structure, and is referred 

 to that fiiniily, but it has more complex premolars than the existing 

 moles. 



The recent genus Gyrnnura agrees very well with Leptictis with 

 regard to the condition of the premolars, the last one in each jaw 

 having the elements of the molar crown. 



IV. CARNIVORA. 



In this group, the premolars never acquire any very great degree 

 of complication. In the Pinnipedia the molars and premolars are 

 very much alike, though this is due rather to a simplification of the 

 molars than to any complexity in the premolars. These teeth may 

 either be simple conical bodies, as in the Otariidce and hooded seals 

 (Gystoj)})ora), with a crown consisting of a simple cusp and 

 implanted by a single fang ; or, as in the typical Phocidce, both 

 classes of teeth are assimilated to one type, characterized by the 

 suppression of the internal cusps, and the addition of sharp basal 

 cusps on the anterior and posterior edges of the principal cone, 

 which appears to i-epresent the paracone in the upper molars, and 

 the protocone in the premolars of both jaws and the lower raolars. 

 We are, however, as yet entirely ignorant of the phylogeny of the 

 pinnipedes, and cannot therefore very well determine the homologies 

 of these elements. The dentition of the creodont family, Memny- 

 chidce, presents many analogies to that of the true seals, but there 

 can be no question of a genetic relationship between the two 

 groups. 



Fig. 5. 

 Fourth upper premolar of left side, external and crown views. 1, Deltatherium 

 fuiidamniis : 2, Siiiopa ■nj/iiius; 3, Cynodictis gracilis: 4, Felis concolor. 

 Pr protocone, d deuterocone, tr tritocone, ps protostjle. (1 and 2 from the 

 *Cope collection.) 



