MASTODON SIVALENSIS. 131 



tenths in width. That of the upper jaw has six ridges, which are divided Mastodon 



Sivalensis. 



from each other by five transverse furrows ; the sixth is less distinctly 

 separated than the others, and has behind it a trifid talon. The longitu- 

 dinal furrow, separating the external and internal mammilla}, is less distinct 

 than it commonly is in the Mastodon family, in consequence of the mam- 

 milla? inclining towards the median line of the tooth in such a way that 

 the mammilla of one side corresponds with a depression on the other, so as 

 to indigitate. The sixth, not being fully developed, presents, instead of two 

 mammilla?, four small ones, which would undoubtedly have merged in 

 two, had the animal lived longer. The mammillae are of a rounded form, 

 as in the narrow-toothed Mastodons, and not flattened like those of the 

 Mastodon Giganteus. The basal cingulum is remarkably prominent. 



The corresponding tooth in the inferior jaw is, as already said, longer 

 than that in the upper. The number of ridges or lobes is the same, i.e. six, 

 and a talon with one eminence. The basal cingulum is less prominent. 

 The mammillae are more inclined, both longitudinally and transversely. The 

 extremities of the mammillae of the three anterior ridges are worn away in 

 the upper tooth, and of two in the lower, displaying, in the former, oval 

 figures ; in the latter, no distinct form. 



In an excellent cast of a large portion of the head, with the palate 

 nearly entire, there are four teeth, two on each side. One of these is almost 

 perfect : it is the left ultimate molar, and contains five ridges. They have 

 the same form as those described above, but their direction is less oblique. 

 This tooth, except as to the number of its ridges, has a general resemblance 

 to the corresponding tooth of Mastodon Angustidens in the Paris Museum ; 

 but the clefts between the ridges are not so deep as in the latter. It is 

 not at all worn. In front of it is the penultimate molar, very much worn ; 



