ELEPIIAKT AND MASTODON. 89 



coTild establisli the case would be the finding of an nnkncwn 

 tooth in front of the third milk molar. But, so far as we are 

 aware, no instance of this sort has been recorded, notwith- 

 standing the great number of young specimens which have 

 been described by different observers ; and the result of the 

 whole evidence at present is, that, ordinarily, the premolars 

 are entirely suppressed in M. Ohioticus, in both jaws. 



There is nothing, therefore, in the mode of succession of 

 the teeth in this species, to show where the deciduous series 

 terminates and the true molars begin. The last milk molar 

 is followed in antero-posterior succession, as in Dinotlierium, 

 by a tooth which has its crown divided also into three ridges, 

 and is thus indicated to be the antepenultimate, or first true 

 molar. It measures four inches long, by about three in width, 

 differing only m size from the tooth which precedes it. The 

 penultimate, or second true molar (being the fifth in the 

 order of succession), consists also of three ridges, and mea- 

 sures about five inches by three and a half. The third, or 

 last true molar, consists of four principal ridges, and a small 

 heel ridge, which varies considerably in amount of develop- 

 ment. This tooth measures 7*25 inches or upwards, by about 

 4*5 in width. 



The inferior true molars in M. Ohioticus, agree with the 

 upper in the form and division of their crowns, except the 

 last, which has usually five prmcipal ridges. They are 

 narrower in proportion to their length, and the subordinate 

 talon ridges are more developed. The molar formula in this 

 species is, therefore, 3 milk molars in the young animal ; and 

 premol. + 3 true molars = 3 in each side of both jaws of the 

 adult; the number of ridges in the different teeth, accord- 

 ing to their succession, being „'^„"*"„ in the milk molars, and 



3 + 3 + 4 "-'/-t-4 + d 



^-— — ^ in the triie molars. With regard to the number of 



6+6+0 ~ 



teeth which are simultaneously present in the jaw; the lower 

 jaw of Tetracaulodon figured by Godman,' shows the three 

 milk molars in use, and the first true molar in its alveolus, 

 there being four out of the whole number of six teeth at one 

 time in the jaw. These are ultimately in advanced age 

 reduced to the last tooth, the others being shed. 



Jf. angustidens. — The dentition of M. angustidens is in- 

 volved in great confusion, in consequence of most authors 

 who have written on this species having mixed up, under 

 this name, two distinct forms, the one characterized like M. 

 Ohioticus, by a ternary, the other, by a quaternary division, in 

 the ridges of the middle teeth. It will be necessary to 



' Amer. Plul. Trans. Now Series, vol. iii. pi. xviii. 



