PROGRESS IN VERTEBRATE PALAEONTOLOGY 455 



the British Museum (Natural History). The features distinguish- 

 ing the species from its ally, the living pigmy hippopotamus of 

 Liberia (H. liberiensts), are indicated in this communication. 



Going still farther south, special interest attaches to a note 

 by Dr. R. Beck, in the serial last mentioned (pp. 49-50), on a 

 fragment of the tooth of a mastodon from Barkly West, South 

 Africa. Assuming it to be authentic, this specimen affords the 

 first evidence of the occurrence of this group of Proboscidea in 

 Africa south of the Sahara, and has an important bearing on 

 distribution. 



Two papers — in addition to the one by Mr. Tomes already 

 cited — on the subject of teeth claim brief notice. In the first of 

 the twain, published in the Proceedings of the Washington 

 Academy of Sciences (viii. pp. 91-106), Mr. J. W. Gidley confirms 

 the opinion of certain other observers that the cusps which go 

 to form "tritubercular" molars are by no means homologous with 

 one another in different genera of fossil and recent mammals. 

 Nevertheless, despite the fact that the " protocone " may not be 

 the original primary cusp, the author advocates the retention of 

 Prof. H. F. Osborn's names for the cusps of the tritubercular 

 molar. In this we venture to think he is wrong. The names 

 are cumbrous and difficult to assign to their respective positions ; 

 and if they do not represent homologous elements, the sooner 

 they are consigned to oblivion, and replaced by the older terms, 

 the better. 



The second of the two papers on dentition is one by Dr. O. 

 Abel, of Vienna, on the milk-molars of recent and fossil sea-cows 

 (Sirenia), published in the second volume of the Neues Jahrbuch 

 fur Mincralogie, etc., for 1906. The author has been enabled to 

 demonstrate that the sea-cows, although now monophyodont, 

 were originally diphyodont, and that the reduction of the 

 dentition commenced with the posterior premolars. 



Finally, in the Comptes Rendus of the Paris Academy 

 (cxlii. p. 610) Mr. C. Deperet directs attention to the important 

 influence which ancient migrations have had on the evolution 

 of mammals. 



Turning to work on fossil reptiles, a brief reference will 

 suffice to Dr. W. J. Holland's memoir on the dinosaurian 

 Diplodocus {Mem. Carnegie Mus. Pittsburgh, ii. art. 6), in which 

 special reference is made to the model of the skeleton recently 

 set up in the Natural History Branch of the British Museum. 



