1922] Kellogg: Calif ornian Forms of Microtus Montanus 



253 



molars, and for that reason the internal portion of the anterior trans- 

 verse loop would be the protoconule instead of the parastyle. The 

 protoconule is a cusp which is present in the early stages of develop- 

 ment of the mammalian molar crown, whereas the parastyle is a later 

 addition, or specialization. 



TABLE III 



Table showing correlation and allocation of the second upper molar and the fourth lower premolar 

 in thirty-two slcuUs, each being referable to six types of variation in enamel pattern, illustrated in 

 the text-figures as lettered. 



There are also additional or supernumerary loops present in the 

 fourth lower premolar which are very difficult to homologize. The 

 sequence of their succession is uncertain and they have therefore 



