1922] Kellogg: Calif ornimi Forms of Microtiis Montanus 251 



410-417). The evidence adduced by Mahii was derived from the 

 resemblance in form of the second upper molar to the fourth lower 

 premolar, and from the assumption that in Arviool>a the position of 

 the cement bands on the teeth indicates the homologous crown divi- 

 sions. Forsyth-Major {loc. cit.) also used numerals in his studies on 

 various groups of rodents. Most of the crown divisions in the molars 

 of Oryzomys as figured by Goldman (1918, p. 11) are present in the 

 hypsodont teeth of Microtus. 



pm, 



m, 



m. 



pm' 



A B 



Figs. A, B. Diagrams of enamel patteras of left lower and left upper molari- 

 form series of Microtus montanus yosemite. X 6. Mus. Vert. Zool., no. 22365, 

 c?; Tuolumne Meadows, Yosemite Park, California. 



Explanation: Pm4, fourth premolar; Ml, first molar; M2, second molar; end, 

 eutoconid; esd, entostylid; hy., liypocoue; hyd, hypoeonid; me., metacone; med, 

 metaconid; niesd, mesostylid; m\., mctaconule; mts., metastyle; pa., paracone; pad, 

 paraconid; pi., protoconule; pr., jjrotocone; prd, protoconid; prcd, protoconulid ; 

 ps., parastyle; sec. ml., secondary metaconule; sec. pad, secondary paraconid; sec. 

 prcd, secondary protoconulid. 



It is not the writer 's intention to take up any theoretical discussion 

 involving the origin of the various cusps, for that can be accomplished 

 better by some one having more material, especially fossil material, 

 at his disposal. However, there are one or two points that might well 

 be mentioned in connection with the present diagrams (figs. A to D), 



The entire loop anterior to the protocone in fourth upper premolar, 

 which was designated by Winge as "1" (= parastyle), cannot be 

 designated as that cusp with any degree of certainty because of its 

 direct connection with the protocone. The parastyle is a direct off- 

 shoot of the paracone. It may be possible, however, that the parastyle 

 loses its connection with the paracone and unites secondarily with the 

 protocone. The data which are available relative to the sequence and 



