134 R. BROOM. 



the protocoiie, but it was the antero-external cusp in the 

 premolar that was given the same name, and when the 

 premolar becomes quite molariform we have the unfortunate 

 confusion as seen in Hyracotherium, that the last premolar 

 and the first molar, though almost identical in structure, have 

 all the main cusps diiferently named. 



Huxley, Wortman and others have maintained that the 

 molars and premolars have developed in a similar fashion and 

 only differ in the molars having usually become more complex. 

 In Chrvsochloris the premolars are so nearly similar to the 

 molars that no person could tell readily whether a detached 

 tooth were a molar or premolar, and it is very difficult to 

 doubt that the cusps of the one are homologous with the 

 similarly situated cusps of the other. If the premolar 

 analogy theory is correct — and to my mind the case for it 

 seems very strong — then the premolars and molars of C h r y s o - 

 chloris can be described as consisting of a high main cusp 

 near the inner side of the tooth connected with two smaller 

 external cusps and forming with them a narrow trigon, and 

 with a small internal cusp low down on the side of the main 

 cusp. 



When we endeavour to identify these cusps we find it 

 impossible to be dogmatic. The small internal cusp, however, 

 we can, I think, identify with certainty. It meets the talonid 

 of the lower molar in much the same way as the inner cusp of 

 Dasyurus meets the talonid, and hence must be the cusp 

 that is called protocone. Not that it corresponds to the 

 reptilian cone, but because the name "protocone" has come 

 ■to be attached to the antero-internal cusp of the mammalian 

 molar and seems likely to stick to it, even though the reason 

 for giving the name be wrong. As I do not feel justified in 

 opposing the current names, I am provisionally accepting the 

 names of the molar cusps and transferring them to the pre- 

 molars, though one would prefer to call the main one the proto- 

 cone. 



The next homology one has to try and settle is that of the 

 main cusp, and tlie first question that arises is whether it cor- 



