NO. :!113. EXTINCT ^IRENIAN DESM0STYLU8 HESPERUS— HAY. 391 



In none of the teeth figured by Yoshiwara and Iwasaka are there 

 more than ten pillars, and not so many appear in any tooth of the 

 specimen at hand. 



As to the number of teeth of each kind we are not yet wholly 

 certain. The Japanese authors were fortunate in having the anterior 

 half of both rami of the lower j aw. On each side of this they found 

 two straight, forwardly directed, tusk-like teeth, which they inter- 

 preted as the first and second incisors. The length was believed to 

 be about 200 mm., and the diameter about 31.5 mm. Inasmuch 

 as the lower jaw is missing in the Oregon specimen no comparisons 

 can be made. 



In the front part of the upper jaw the Japanese specimen pre- 

 sented, within the somewhat injured maxilla of the left side, a tooth 

 resembling the tusk-like teeth of the lower jaw and,hke them, directed 

 foi'ward; but it had not been extruded. The describers concluded 

 that it was an incisor. However, this tooth appears to be inclosed 

 principally in the maxilla, near the premaxillo-maxillary suture, and 

 it is more probable that it was a canine. In Prorastomus there were 

 weU-developed canines above and below. In the upper jaw of 

 Eosiren ^ there was a small canme and apparently small second and 

 third incisors. There was, on each side, in the genus just men- 

 tioned, a large first incisor, as there is in Halicore; but it was at 

 the end of the snout. In Halicore this tooth is wholly in the pre- 

 maxiUary. It seems most probable that the large upper tusk-like 

 tooth of Desmostylus is a canine and that in the Japanese specimen 

 it was destined to remain in the jaw, as the great first incisor of the 

 female Halicore does. In the upper jaw of our specimen of Des- 

 mostylus, on the right side, there is present what seems to be the 

 base of the upper tooth supposed to be a canine. All that is present 

 hes behind the suture between the premaxilla and the maxilla, and 

 it is badly eroded. In case the upper tusk-like tooth is a canine, 

 it is probable that the hinder of the lower ones is also a canine. 

 The other one is probably a third incisor, inasmuch as it is far removed 

 from the midline of the front of the jaw. 



Yoshiwara and Iwasaki found in the upper jaw, far behind the 

 tusk, a tooth composed of four cyhndrical pillars, varying in diam- 

 eter. This tooth, about 22 mm. long and 24 mm. wide, was regarded 

 by them as the second premolar; and there were reasons for beheving 

 that there was another front of it, pm^ ?. Inasmuch as these teeth 

 are immediately in front of a molar and there is a great space in 

 front of them which might, in some ancestor at least, have been 

 occupied by premolars, there seems to be little reason for not regard- 

 ing them as pm^ and pm*; imless, indeed, as may have been the 



' Audrews, Catalogue of the Tertiary A'ertebrata of the Fayum, Egypt, p. 203, pi. 20, fig. 1. 



