22 PACHYDERMATA. 



indicated by Croizet and Jobert, he states that M. Arvernensis is 

 distinguished from M. maximus (M. Ohioticus), M. angustidens, 

 and all the other species then known, by the circumstance that the 

 third molar in the order of antero-posterior succession has the 

 crown divided into four ridges, while the same tooth in the other 

 species presents only three ridges. In a subsequent memoir, 

 on the fossil remains of Georgensmiind, 1 von Meyer figured and 

 described several Mastodontine grinders, which he referred to the 

 true M. angustidens of Cuvier, and which confirmed the con- 

 stancy of the differential character between that species and M. 

 Arvernensis, in the numerical division and form of the crown 

 ridges, as pointed out by him in his previous memoir. This was 

 the first step towards a satisfactory determination of the species, as 

 distinct from M. angustidens ; and a great mass of additional mate- 

 rials, confirming the same inference, was soon afterwards brought to 

 light by Dr. Kaup ; but, in the interim, new observations, of 

 great interest, were made upon the Mastodon of North America, 

 which gave an entirely different character to the investigation from 

 this date. 



No suspicion appears to have been entertained before this time, 

 that any of the Mastodons, more than the existing Elephants, pos- 

 sessed tusks in the lower jaw. Cuvier expressly affirms their 

 absence, 2 although, as has been observed by Professor Owen, 3 he 

 figured in the original memoir in the ' Annales du Museum,' and in 

 the first edition of the ' Ossemens Fossiles,' a lower jaw of an adult 

 Mastodon, showing what appears to be the alveolus of a persistent 

 inferior tusk. Early in 1830, a memoir by Dr. Godman was 

 read to the American Philosophical Society, 4 upon a Mastodontoid 

 lower jaw, with two small tusks, which he described as characteriz- 

 ing a distinct Proboscidean genus, under the name of Tetra- 

 caulodon. This jaw belonged to a young animal, and showed four 

 molars on each side, the anterior two of which Godman considered 



1 Museum Senckenbergianum. Die fossilen Zahne und Knochen von Georgensmiind, 

 1834, p. 33, Tab. 1 and 3. 



3 Oss. Foss. torn. i. p. 233. 3 Owen, ' Odontography,' p. 619. 



4 Godman, * Americ. Phil, Trans.' New Ser. vol. iii. p. 478. ' Tetracaulodon Masto- 

 dontoideum.' 



