410 



University of California Publications. 



[Geology 



In the specimen of Desmostylus described by Yoshiwara 

 and Iwasaki there was a single pair of large tusk-like teeth 

 in the upper jaw and two pairs in the lower jaw (figs. 10 



and 11). The tusks were considered 

 as incisors. The upper pair seems, 

 however, in doubtful relation to the 

 maxillary, and may represent canines, 

 as also the posterior lower pair. The 

 tusks are said to reach a length of at 

 least twenty centimeters. They are 

 circular in cross-section, and are en- 

 tirely covered with a thick enamel 

 (figs. 8 and 9). 



As nearly as can be determined, 

 the tusk fragment obtained by Robert 

 Anderson and R. W. Pack from the 

 Vaqueros formation of California corresponds in form and struc- 

 ture to the tusks of the Japanese specimen of Desmostylus. It 

 was about eighteen inches long, and was completely covered with 

 enamel. Only the tip was preserved in the collection examined 

 by the writer. This fragment is about one inch in diameter at 

 a point less than two inches from the tip. The enamel on this 

 tooth is slightly roughened. 



SKELETON 



The skull of Desmostylus is known only through the specimen 

 described from the Tertiary of Japan. The posterior region 

 of the skull is broken away. The superior side from the frontals 

 forward as represented in the illustration presented by Yoshi- 

 wara and Iwasaki (fig. 10) differs from all of the known sirenian 

 forms. The premaxillaries completely surround the anterior 

 narial opening, their posterior ends separating the acute an- 

 terior terminations of the nasal elements from the posterior 

 border of the nares. The exact form of the nasals is not quite 

 clear, but from the illustration they seem to extend backward 

 between the anterior ends of the frontals. The maxillaries are 

 large elements, forming a considerable part of the facial region. 



Figs. 8 and 9. Desmostylus, 

 sp. Incisors in cross-section 

 in the jaws, X Vi- Miocene 

 of Japan. Fig. 8, upper in- 

 cisors; fig. 9, lower incisors. 

 (After Yoshiwara and Iwa- 

 saki.) 



