1922] 



Kellogg: Synopsis of Microtus Mordax 



279 



Q 



R 



S 



T 



Figs. Q-T. Diagrams of enamel pattern of fourth lower premolars of Microtus 

 mordax sierrae. X 6. Fig. Q, no. 22383, ^, Mus. Vert. ZooL, Merced Grove Big 

 Trees, Mariposa County; fig. E, no. 22384, J, Mus. Vert. Zool., Merced Grove Big 

 Trees, Mariposa County; fig. S, no. 22382, J, Mus. Vert. Zool., Merced Grove Big 

 Trees, Mariposa County; fig. T, no. 22446, $, Mus. Vert. Zool., head of Lyell Canon, 

 Yosemite Park, Tuolumne County. 



u 



V 



w 



X 



Y 



Figs. U-Y. Diagrams of enamel pattern of second upper molars of Microtus 

 mordax angusticeps. X 6. Fig. U, no. 11 528, ^, Mus. Vert. Zool., 3 miles west 

 of Areata, Humboldt County; fig. V, no. 11.526, J, Mus. Vert. Zool., 3 miles west 

 of Areata, Humboldt County; fig. W, no. 20103, 5? Mus. Vert. Zool., Mendocino 

 City, Mendocino County; fig. X, no. 1725, J, coll. A. B. Howell, Crescent City, Del 

 Norte County; fig. Y, no. 25588, 5j Mus. Vert. Zool., Fort Bragg, Mendocino 

 County. 



Z AA BB 



Figs. Z-BB. Diagrams of enamel pattern of second upper molars of Microtus 

 mordax hernardinus. X 6. Fig. Z, no. 6264, J', Mus. Vert. Zool., Bluff Lake, 

 San Bernardino Mountains; fig. AA, no. 6299, $, Mus. Vert. Zool., San Bernardino 

 Mountains; fig. BB, no. 6290, j?, Mus. Vert. Zool., San Bernardino Mountains. 



As a further illustration of the amount of variation likely to be 

 encountered, attention should be called to the incisive foramina 

 exhibited by the skulls on plate 8. The expansion or contraction of 

 these foramina is subject to considerable variation. In fig. 7&, the 

 incisive foramina are narrowly constricted posteriorly as in Microtus 

 montanus, while in fig. 3& they are wide open. Other individual differ- 

 ences are normally present in an ordinary series. For instance, the 

 sides of the foramina are nearly parallel in fig. 5&, and a further type 

 of modification with both ends narrowed is shown in fig. 8&. 



