MOLAR TEETH OF THE MAMMALIA EDUCABILIA. 257 



Fig. 30. — Microsyops elegans. 



similar to the type [i. e., pattern] of the genus Mastodon [Stego- 

 don] and others of the beginning of the series. The deposit of 

 cementum takes place later, till the valleys are entirely filled 

 up. Thus the relations of this 

 part of the tooth structure in 

 the series are also those of the 

 successional growth of Elephas 

 or the extreme of the series." 

 The transition from the 

 bunodont type to the lophodont in the mandibular dentition is 

 seen in the Eocene genera Microsyops and Limnotherium, where 

 the opposite cones are connected by a low cross-crest. 



n. Amcebodonts; ^nnodiovit tj^Q Hyopsodus.* 



4. Symhorodonts. — In Hyopsodus the exterior cones are already 

 somewhat excavated on the inner side, so that a section of each is 

 somewhat triangular. It is obyious that but little more compres- 

 sion and curvature are required to produce the type of Palmosyops, 



Fia. 31. — Hyopsodus. 



Fig. 33. — AncMppodus. 



Fig. 32. — Palaosyops Icevidens. 



Fig. 34. — Palceosyops. 



etc. (Fig. 32). The angles of the outer cones in Hyopsodus are 

 also slightly produced as low ridges to the bases of the alternating 

 tubercles of the opposite side : the elevation of these ridges is only 



* I orif^inally (" On the Primitive Types of Mammalia Educabilia," p. 9 ; " Ilay- 

 den's Geoiog. Survey Terr.," 1872, 1873, p. 648) selected Pliolophus ( Oligotomus Cope) 

 for this position, but as it has a considerable diastema, it is better exchanged for 

 Hyopsodus, where the dental series is uninterrupted. 

 17 



