274 



MASTODON. 



ing up that part of the valley which lies between them, 

 while the inner pair of points, belonging to each ridge, 

 is free from accessory tubercles, thus leaving the portion of 

 the divided valleys between the inner points open. A small 

 anterior talon, running outwards, descends around the base 

 of the outer tubercle of the front ridge, and a larger posterior 

 talon, composed of two or three tubercles, is appended to the 

 posterior end of the outer division of the last ridge, but free 

 from any connection with the inner division of the same 

 ridge. The tooth, therefore, belongs to the sub-genus Trilo- 

 phodon, and to that section of it which may be characterized 

 by ' Colliculi obtusi, valliculce interrupts' The necessary 

 consequence of the form of the crown, as above described, is 

 that in the progress of wear, when the ridges are ground 

 down, the outer pair of points with its outlying appendages 

 must yield a trefoil or complex pattern to the disc of 

 abrasion ; while the inner pair, being simple, would yield an 

 elliptical and transverse disc, free from any complication. 

 This is the character which distinguishes Mastodon Andium 

 from Mastodon Humboldtii. As these species are but imper- 

 fectly known in England, and one of them still more imper- 

 fectly represented by specimens, a few remarks upon them 

 may not be considered out of place on the present occasion. 

 Although these names were vaguely imposed by Cuvier, we 

 are indebted to Laurillard x for the first accurate definition of 

 their distinctive characters, which has been confirmed by 

 Gervais, from the fine series of remains brought by Weddell 

 from Bolivia. 2 Both belong to the subgenus Trilophodon. In 

 M. Humboldtii, both the inner and the outer divisions of 

 each ridge are flanked by outlying tubercles, so that the 

 valleys are blocked up, and the mammillae being channelled 

 vertically, a very complex pattern is yielded by the discs of 

 wear ; two trefoils are produced, separated by a cleft, some- 

 what as in the molars of Hippopotamus, or, as it has been 

 happily expressed by Gervais, ' Deux figures en trefle adossees 

 par leur base.' 3 The valleys are covered with a thick coat 

 of cement, and the lower jaw is destitute of an incisive 

 beak. In M. Andium there is but a single trefoil, accom- 

 panied by an elliptical transverse disc to each ridge, the 

 valleys are sparingly invested with cement, and the symphy- 

 sis of the lower jaw is produced into a long massive and 

 deflected incisive beak, as in Mastodon angustidens. This 

 beak, as shown by the young animal, is figured by Laurillard 

 in d'Orbigny's ' Voyage ; ' and I have seen at Geneva the cast 



1 Alcide d'Orbigny's ' Voyage dans Fossiles de l'Amerique Meridionale.' Ex- 

 l'Amer Meridiem.,' Geol. p. 144, Pis. x. pedition de Castelnau, 1855, p. 14, 

 and xi. ; and Diet. Univers. d'Hist. PL v. 



Natur. torn. viii. p. 30. 3 Op. cit. p. 18. 



2 ' Eecherch. snr les Mammiferes 



