616 UNGULATES. 



The deciduous formula, is : — 



incisors — : molars — : = 16. 



1-1 ' 3-3 



^1 



226. Mastodon giganteus. — T shall first describe the molar teeth in 

 the Mastodon giganteus, as these best exhibit the tapiroid character of the 

 grinding surface. This character is most strongly manifested, agreeably 

 with the law which has been so frequently illustrated in the present 

 work, by the molars which are first developed in the young animal, at 

 the period of dentition when it has receded least from the common 

 type. The crown of the first deciduous molar in the lower jaw 

 (PI. 144, fig. \, d 1) is subquadrate, one inch four and a half lines 

 in antero-posterior diameter, one inch three lines across its broadest 

 part ; it supports two transverse ridges, the anterior one most deeply 

 cleft into two mastoid eminences, the posterior and broader ridge 

 having one angle produced forwards : the front, back and outer 

 part of the bases are girt by a tuberculate ridge ; the whole is sup- 

 ported by two long subcompressed divergent fangs. (1) 



The second deciduous molar (PL 144, fig. 2, d 2) has a crown, 

 like the first in shape, but measuring one inch eleven lines, by 

 one inch eight lines, and having both transverse ridges subdivided 

 into two mastoid eminences, and a larger posterior basal ridge ; 

 it is supported by two fangs. (2) It is displaced and succeeded ver- 

 tically by a tooth (ib. fig. 3, p 1) of a more simple form, having 

 a crown broader in proportion to its length, supporting two bifid 

 transverse ridges, and girt by a basal cingulum ; it measures one 

 inch five lines by one inch four lines. This tooth may be regarded 

 as the first of the theoretically permanent or adult series of teeth : 

 it answers to the penultimate premolar in the Dinothere and Tapir, 

 but is very soon shed. 



The tooth (ib. figs. 4 & 5, d 3) which answers to the last 

 milk molar in the above cited Pachyderms, rises into place and 

 use, as in these and other Quadrupeds, before the premolar is 

 developed : its crown supports three bifid transverse eminences, 



(1) On this tooth is founded the nominal species Mastodon tapiroides of Koch and 

 Grant. Geol. Proceedings, vol. in, p. 771, It is figured on the left side of the lower jaw 

 of the young Mastodon referred by Godman to the Tetracaidodon, loc. cit. PI. 18. 



(2) This tooth is also figured in the Plate above cited of Dr. Godman's Memoir. 



