\0 AKT. iV— S. YOSHIWAKA AND .r. IWASAKT. 



peculiar lunii iviniiids iis of the most priiiiiti\'e teeth of Mastoiloii. 

 The u'reat elongution of hoth jaws which are narrowed and quite 

 flattened, the anterior position of the nasal foramen, and the much 

 narrowed and compressed roots of the teeth are cliaracters quite 

 different from those of Proboscidea, if we except some very aberrant 

 forms. In the Japanese form, the enamel is thick and covers the 

 whole surface of tlie incisors. Sucli a case is never found in the 

 hitherto described Proboscideans ; Stcgodons^ most Klephas and the 

 I'Jiocene Mastodons having no trace of enamel. The only cases in 

 wliich tlie presence of enamel lias been ascertained are those of 

 some ]\Iiocene species of Mastoilons, and of some FAeplias. Put in 

 the former the enajnel covers only the lateral side of the tusks as a 

 longitudinal band, and in the latter it covers only the apex of the 

 teeth which, liow^ever, soon wears away. Thus the great number of 

 thickly enamelled small incisors and the most primitive form 

 of premolars and molars which are all siinultaneouslv functional, 

 are the characters which make the Japanese fossil approach to the 

 primitive Ungulata, from which Proboscidea is supposed to have 

 descended. Our form also resembles, in some respects, certain Sirenia, 

 viz., in the structure and number of incisors, in the bunodont character 

 of the molars, in the thinning out of both jaw bones anteriorly, 

 and in the protrusion of the upper jaw over the lower. &q. It is 

 true that Sirenia has a close relationship with the Lngulata; its 

 most primitive form, Vronistouius, having a great number of incisors, 

 a pair of canines, and a smooth, straight and slender up])er jaw, all 

 whicli cliaracters decidedly show its descent fn^ni an L ngulata like 

 J'lieiiacodit.s or 'I'dpirus. [.vdkkkkk is of oftinion that llalithcvium 

 raronense Zk;. is a form which has descended from an artiodactyle 

 Unofulata with short-crowned and solenodont molar teeth. Zittel 

 also mentions that the molars of Sirenia resemble partly those of the 



