771 
which are compared with those of the elephant and other allied ge- 
nera. ‘The fifth section of the memoir is occupied with the descrip- 
tion of the development, forms, structure and changes of the dental 
system of Mastodontoid animals ; and each tooth and tusk of the 
three principal genera are described and compared, and the principal 
modifications they exhibit according to difference of age, sex, and 
species. After pointing out the necessity of including the entire se- 
ries of successive teeth, in the dental formula of genera, where the 
teeth are constantly displacing and succeeding each other through 
the whole of life, the author announces the dental formuls of the 
four Proboscidian genera of Pachyderma to be 
E 2 0 8 —8 
Elephas, Inc. can. GH mol, 92g: = 34. 
2 0 6 —6 
Mastodon, Inc. 92 can. a mol. 626 = 26. 
‘ 2 0 6 — 6 : 
Tetracaulodon, Inc. >> can. mol. Gis Gh 28. 
: = §) 
Deinotherium, Inc. 2 » Can. 0 5 mol. Foils in == DY). 
For the determination of the dental formule of Mastodon and Te- 
tracaulodon, Dr. Grant relied entirely on the splendid collection of 
jaws, crania, and teeth in Mr. Koch’s possession, which afford ample 
means for the solution of that problem. For the dental formula of 
Deinotherium he has been indebted solely to the casts and fragments 
of that genus in the British Museum. After explaining the uncer- 
tainties and fallacies to which naturalists have been exposed in the 
identification of species, from not having ascertained the entire dental 
series in any Mastodon, the sixth section of the memoir describes the 
distinctive characters and the distribution of the Mastodon angusti- 
dens, M. latidens, M. Elephantoides, M.minutum, M. Tapiroides, M. 
Andium, M. Borsoni, M. Humboldtii, M. Turicense, M. Avernense, 
M. giganteum, M. Cuvieri, and M. Jeffersoni. The seventh section 
of the memoir is devoted to the examination and description of the 
generic characters of Tetracaulodon, as established by Dr. Godman, 
and as founded onthe number and form of the teeth, the peculiarities 
of their microscopic structure, the form of the jaws, the tusks, the 
alveoli of the tusks, the intermaxillary fossa, the infra-orbitary fora- 
mina, and other influential characters. The eighth and last section 
of this paper is occupied with an account of the distinctive characters 
and the distribution of the known species of this genus ; viz. Tetra- 
caulodon Godmani, T. Collinsii, T. Tapiroides, T. Kochii, T. Haysu, 
and 7, Bucklandi. 
VOL, 11%, PART 11, 3k 
