Vol. 6] 



Merriam: Notes on Desmostylus. 



409 



segment of the tooth. A third upper cheek-tooth, M 2 , not yet in 

 function, is seen in the jaw bone behind M 1 . 



In the lower jaw (figs. 5 to 7) there is less difference between 

 the first and second cheek-teeth than in the upper series. The 

 first two teeth, considered by Yoshiwara and Iwasaki as P 3 and 

 P 4 , each consist of seven pillars, but P., is much the smaller tooth, 

 and is short-elliptical instead of long-quadrate in cross-section. 



M 1 



Figs. 4 to 7. Desmostylus, sp. Cheek-teeth in occlusal view, X %. 

 Miocene of Japan. Fig. 4, M 1 and P J ; fig. 5, M t ; fig. 6, P 4 ; fig. 7, P.. 

 (After Yoshiwara and Iwasaki.) 



P 4 consists of three transverse rows of pillars with two each in 

 the anterior and middle segments, and three in the posterior one. 

 P 3 may be considered as having three transverse rows of two 

 each with an isolated pillar at the anterior side of the tooth. 

 The third lower cheek-tooth, M 1? consists of only six pillars ar- 

 ranged in three transverse pairs, but it is much larger than the 

 second tooth, or P 4 . 



As the Japanese specimen evidently represents a young indi- 

 vidual, it is not entirely certain how many cheek-teeth were 

 present normally in the jaw of the adult animal. 



