36 ELEPHANTS. 



above, p. 8) fills the transverse valleys in the crowns of the 

 molars (fig. 23). In Elephas (Steyodori) clifti the number of 

 ridges is greater than in Mastodon latidens. In order to express 

 briefly the number of ridges in the molars of this and other species, 

 a formula is used, thus : in E. (Steyodon) clifti the formula 

 M 1 ~, M 2 , M 3 J=|, means that in the first true molar (M 1) 

 there are in the upper jaw 6-7 ridges, while in this case the 

 number in the lower is not known. In the second molar (M 2) 

 there are 6 in the upper, the lower being uncertain, while in 

 the last molar (M 3) there are 7-8 ridges in both the upper and 

 lower jaw. It will be seen, therefore, that the numerator of the 



Fig-. 22. 



G rinding-surface of an upper molar tuoth of Elephas (Stegodon) clifti. From 

 Lower Pliocene, Siwalik Hills, India. Showing six transverse ridges. 



fractions represents the number of ridges in the upper teeth, 

 the denominator the number in the lower. When the two 

 numbers are given thus, 6-8, it means that the number of 

 ridges varies between them. This formula will be employed 

 below in describing the molars, and a table showing the gradual 

 increase in the number of ridges will be given at the end. 



In E. clifti premolars are still developed, but must have 

 been pushed out almost as soon as the milk-molars they replace. 

 The crowns of the molars are quite low, and there is only a 

 small quantity of cement in the valleys between the ridges. 



In Elephas (Steyodori) bombifrons andE. (.) insiynis (fig. 23), 



