132 B. BROOM. 



inately the talon rises to one third of the height, and the 

 para- and nietaconids to two thirds of the height of the 

 protocone. 



In C. obtusirostris the first premolar is distinctly molari- 

 forni in both upper and lower jaws. The upper has no trace 

 of a protocone, and the other molariform teeth have a much 

 smaller protocone than in other species. The lower premolars 

 have s'ot a small talonid, and in the first molar this is rudi- 

 mentary and in the second absent. 



The premolars are practically identical in structure with 

 the molars in both upper and lower jaws. Even the incisors 

 and canines seem to foreshadoAv the cusp development of the 

 molars, and one is irresistibly, driven to the conclusion that 

 the main cusps are homologous throughout. Whether the teeth 

 are degenerate or not does not affect the question, at least in 

 so far as the lower teeth are concerned. And as the milk 

 premolars and permanent premolars are practically identical 

 it does not matter which Ave consider, but as in all species 

 apparently the milk set are the set which serve the greater 

 part of the animal's life — certainly in C. villosa, C. asiatica, 

 and C. hot ten tot a — we may as well confine our attention 

 to merely the milk set. 



When we look at the lower canine first premolar and 

 second premolar we clearly see how the cusps develop. The 

 main cusp or protocone we may safely regard as homologous 

 in each. The feeble posterior basal ledge in the canine 

 becomes the talonid in the premolars. The feeble cusp behind 

 and internal to the protocone of the first premolar becomes 

 the well-developed metacone in the second premolar, and the 

 minute anterior cusp becomes the paracone. The molars are 

 all of the same pattern — three elevated cusps forming a 

 trigonid, and a distinct though small talonid. The interesting 

 thing about such a tooth is that it is identical in almost every 

 respect with the molars of many of the Jurassic and Cretaceous 

 mammals, and also very similar to those of many of the 

 primitive Eocene types. The lower molars of Amphithe- 

 rium only differ slightly in the relative proportions of the 



