1884.] NEW YORK ACADEMY OF SCIENCES. 21 



Elephas Americanus roamed southward and northwestward from 

 the Gulf of Mexico to Alaska. It had fewer plates of enamel 

 in the molars, and the tusks were straighter. Some paloeontolo- 

 gists regard it as only a moditi cation of E. prhnigenius. 



Fourteen extinct species of Elejphas are kno^vn, and about 

 twenty species of Mastodon. 



Description of Elephas. — There are two living species, the 

 Indian and African, which are but a remnant of the host of 

 earlier times. 



Feet : Toes, five ; outer pair more or less rudimental ; nails, 

 in the Indian, five and fom*, in the African, four and three. 



Tasks : Enamel confined to apex and sooi» worn away. In 

 the Mastodon, the enamel was in longitudinal bands. The tusks 

 are developed in the premaxillse, but for solid support sink into 

 specially developed aveolar processes of the maxillie. The 

 curvature and size vary somewhat according to the food. De- 

 ciduous tusks appear from the fifth to the seventh month, about 

 two inches long and one-third inch diameter. They are shed 

 before the second year. The permanent tusks grow two months 

 later. 



Molars show a modification from those of the Mastodon, 

 similar to the change from the PaUeotherium to the horse. 

 Occasionally a rudimentary molar is found in front, which 

 makes the typical seven. Only the last three are true molars. 

 These teeth are replaced horizontally, and only one or a portion 

 of two are in use at once. The dental changes require the entire 

 life of the animal. The other extreme is found in Dinotherivm, 

 wliere all the molars are in use at once, and the milk molars are 

 displaced vertically. Mastodon exhibits a transitional form. 



The molars consist of vertical plates of dentine, covered with 

 enamel and solidified by cementum. As the wear comes first 

 on the anterior portion of the crown, the corresponding part of 

 the root is absorbed, which thus permits the pushing forward of 

 the tooth. 



E. Africanus has lozenge-shaped divisions of the crown, with 

 fewer and larger plates and thicker enamel than those of E. 

 Indicus, which has the plates thin and parallel. E.jyr mil genius 

 had the laminae thinner, and rather more numerous than E. 

 Indicus, with the lines of enamel more slender ^md less fes- 

 tooned ; and the molars were relatively and absolutely wider. 



The fir.-t molar, with four plates, appears when the animal is 



