SIWALIK AND NAUBADA PDOBOSCIDIA. 
57—238 
each other. Premolars are common to some Mastodons and one Loxodon {L, platii- 
frons) ; cement is found in the valleys of the molars of M. pandionis, M. humboldtii, 
and M. perimensis, and we have already referred to the mesial cleft and plane of 
wear of the molars in Mastodon and Stegodon. At present, it is true, there is no 
Mastodon known which carries more than five ridges in the intermediate molars, 
but Stegodon cUftii has but six, and is therefore merely the next step in the ascend- 
ing scale towards the true Elephants. The only other point in the dentition of 
Mastodons in which they differ entirely from Elephants, is in the presence of lower 
incisors, but this is only a character possessed by some species of the genus. It 
appears, therefore, that there is no definition by which all Mastodons can be dis- 
tinguished from all Stegodons and the other Elephants ; and although it may be 
desirable to retain these generic (or sub-generic) terms as convenient landmarks in 
the evolutionary series from Mastodon to Elephant, I cannot but think that they 
cannot be philosophically justified, and that all the known Proboscidians, with the 
exception of DinotJierium, ought to be classed in one large genus. ^ 
The line of descent of the true elephants from the Dinotheria has evidently 
gone through some form allied to a Trilophodon of the type of M. tnaximus, then 
through a tetralophodont form like M, latidens, then through the MastodonMke 
Stegodons, like S. cliftii and homhifrons, then the higher-ridged Stegodons, like S. 
insignis, and finally, through the Loxodons. The trilophodont and tetralophodont 
Mastodons, with alternately arranged columns, like M. angustidens and 31. sivalensis, 
belong to a group which seems never to have been further modified in the direction 
of a more complex ridge formula than a pentalophodont type in the true molars. 
It will be noticed in the above descriptions that all the upper milk-molars of 
M. latidens have corrugated enamel, while the lower have the enamel smooth and 
polished. As I have at present only seen one specimen of each tooth (excepting the 
first upper milk-molar), I am unable to say whether this is a constant peculiarity, 
or whether, as is perhaps more probable, there be two varieties of the species, in one 
of which the enamel is smooth and in the other polished. 
Distinctions and differences. — Mastodon latidens does not seem to come close 
to any other species of the genus, the nearest approach being made, in regard to the 
characters of the molars by the European 31. longirostris. The molars of the latter 
species, however, have much taller ridges, with a deeper median cleft, and with acces- 
sory columns partly blocking the bases of the valleys : the series of molars on either 
side of the palate in 31. longirostris do not iucline together anteriorly to tlie extent 
they do in M. latidens. The two species are further widely distinguished by the 
form of the mandible, that of the Indian species being nearly straight interiorly, sub- 
circular in section, with a short and probably tuskless symphysis, v hile that of the 
' On page 12 of a paper on the “ Extinct Animals of North America,” read before the Eoyal Institution on 
March 10th, 1876, by Professor Plower, the author remarks that “ Mastodons, however, were, after all, very like 
Elephants, only being distinguished by some peculiarities of the teeth ; and by means of intermediate species the two 
forms pass so gradually into one another, that it is difficult to say, in the case of some species, with which they ought 
most properly to be classed.” • 
P 
