The elephantoid animal (Mastodon longirostris, Kaup ; Mas todon angustidens, in part, ('uller) which exhibited the above instructive dentition of the proboscidian family, once roamed over the part of the earth now forming England, France, Italy, and Germany. The first steps in our knowledge of its dentition were made by Cuvier, who called it the narrow-toothed Masto don " Mastodon a dents etroites," or Mastodon angustidens. This name was suggested by the less breadth of the grinding surface of the teeth as compared with those of a previously described species of Mastodon from North America, called the Mast.
Dentition of old Mastodon longirosfris giganteus or M. Ohioticus. Cuvier describes and figures a last molar, upper jaw, from Trevoux, consisting, as in the specimen from Norfolk Crag (fig. 113), and as in that from Eppelsheim (fig. 115, in 3), of five transverse ridges, with a front and back talon or subsidiary ridge. The latter is the largest, and sub divided into teat-shaped tubercles, so as almost to merit the name of a sixth division of the tooth. The principal ridges are divided into two chief or primary tubercles, with secondary tubercles in the interspace ; the chief tubercles are more or less deeply grooved lengthwise, or cleft at top, so that masti cation wore them down to small circles of dentine surrounded by a thick border of enamel, and further attrition reduced these to a trilobed or trefoil form.
The last lower molar of the Mast. angustidens from La Rochetta di Tanaro,* exhibits the same five principal trans verse ridges and the hinder one, as in the corresponding tooth in the Eppelsheim Mastodon (fig. 115, m 3), and being the first of the series of narrow mastodontoid teeth to which Cuvier applied the name angustidens, it may be reg,arded as the type of that species. The characteristic premolar of the Mast. angustidens, with a quadrate crown of two ridges, each cleft into two tubercles (fig. 3), is figured by Cuvier, in Op. cit. pL i., fig. 3, and again, in situ, with the last deciduous molar (d 4) in a portion of the upper jaw of the Mastodon angustidens from Dax (ib. pL iii., fig. 2). The nature of this quadrituberculate tooth as a premolar, i. e., as a tooth which displaced and succeeded an earlier or deciduous tooth in the vertical direction, was recognized by Cuvier. " Je crois encore qu'on peut en conclure que la dent anttrieure 6tait susceptible de remplacement de haut ou bas, comme dans l'hippopotame : ma raison est, que cette petite dent de Dax n'est pas encore usee et qu'il Taut qu'elle soit venue apres la grande qui l'est.'t Dr. gaup has described and figured the same premolar in the upper jaw of a younger individual of the Mastodon angustidens (his lcmgirostris), in which it is still concealed in its formative cavity above the three-lobed deciduous tooth which it has replaced in Cuvier's specimen. The tooth next behind, which is the homologue of the last milk-molar (d4, fig. 114) of the
typical series, consists, in both the Dax and Eppelsheim speci mens, of three principal ridges and a posterior bituberculate talon ; this accessory portion being more developed in the Eppelsheim specimen. Whether such difference be valid for a specific distinction may be doubted ; but that Cuvier assigned the name angustidens to a Mastodon with narrower molars than the M. giganteus, which had a quadri-tuberculate premolar, a penultimate molar of four principal divisions and a talon, and a last molar with five principal divisions and a talon, is certain. To that Mastodon, therefore, which has the same shaped and sized ultimate and penultimate true molars and premolar, the same name is here assigned.
The antepenultimate molar (fig. 114, m 2) consists of four ridges and a talon.
Three molars are developed anterior to this tooth ; the first (fig. 114, d 2) is the smallest, with a subquadrate crown of two transverse ridges. The second molar (ib, d 3), of twice the size of the first, has three ridges. The third molar (ib, d 4), with an increase of one-third the bulk of the former, has three ridges and a bituberculate talon, which in some specimens might almost be reckoned as a fourth ridge. The two-ridged premolar (ib.,p 3) above described, takes the place of the second of the above molars, after the first and second are shed. The above definition of the molar series applies to both upper and lower jaws, the cut (fig. 114), and the symbolic letters and numbers, preclude the necessity of verbal description.
From the analogy of the existing elephants, it may be in ferred that the long tusks (fig. 115, t) supported by the pre maxillaries, were preceded by a pair of small deciduous incisors. There is not such ground for concluding their existence in the mandible ; but this jaw, in the male Mastodon longirostth (fig. 115), supported two incisive tusks, shorter and straighter than those above.
In the proboscidian quadrupeds the molar teeth, progres sively increasing in size, and most of them in complexity, follow each other from before backwards, at longer intervals than in other quadrupeds, and are never simultaneously in place. Not more than three are in use at any period on one side of either jaw ; all the molars, save the penultimate (fig. 115, m z) are shed by the time the crown of the last molar has cut the gum, and the dentition is finally reduced to in 3 on each side of both jaws, with commonly the loss of the inferior tusks, as in the old Mastodon turieeneis, from the tertiary deposits of the Po, described and figured by Sis monda.* The genus was represented by species ranging, in time, from the mioceue to the upper pliocene deposits, and in space, cosmopolitan with tropical and temperate latitudes. The transition from the mastodontal to the 'elephantine type of dentition is very gradual.