ADDITIONAL SIWALIK PERISSODACTYLA AND PROBOSCIDIA. 17 
memoir, therefore, the three milk-molars of the elephantine Proboscidia will be 
respectively termed the second, third, and fourth. The same rule will be applied to 
the prcmolars ; the two teeth of that scries usually present being respectively termed 
the third and fourth. This explanation will, it is hoped, obviate any confusion that 
might arise from this change of nomenclature. 
Family : ELE PIIANTIDjE. 
Genus: MASTODON, Cuvier. 
Number of Siivalik species. — In the first volume of this worlP five species of 
Siwalik mastodons were described ; two belonging to the trilophodont, and three to 
the tetralophodont section of the genus. The specimens described in the present 
memoir indicate a third species of the former section ; and illustrate rather more 
fully the dentition of the other Siwalik species of the same section. 
Additional American species.— It may be mentioned that to the list of species of 
mastodons given in the first volume^ there should be added the two following 
undescribed species, viz.'. 
Mastodon {^Tetralophodon) campester, Miocene; N. America. 
Mastodon proavus, Cope.'* Pliocene ; N. America. 
Neiv proboscidian genus. — Since tlie publication of the same volume the tusk of 
a fossil prolioscidian from the tertiaries of Australia has been described by Sir R. 
Owen,^ under the name of Notelephas australis.^ 
Distribution of Indian mastodons. — A very remarkable circumstance in connection 
with the distribution of Indian mastodons is revealed by the specimens described in 
the sequel, and those already described in the first volume of this work. This 
circumstance is that tetralophodont forms are alone found in the typical eastern 
Siwalik Hills, and Burma, while on the extreme north-western side of India, 
trilojihodont are the dominant, or sole, forms.^ It is worthy of remark that 
I inotlierium occurs in the region occupied by the- trilophodons, while the true 
elephants are confined to the tetralophodont region, where the intermediate 
stegodons also 'occur. 
As the dinotheres are essentially European forms, and as there is an Indian 
species {D. sindiense) connecting these with the trilophodons, Avhile it will be shown 
in the sequel that there are good reasons for regarding at least two of the Siwalik 
trilophodons as immigrants into India from the west, it is not impossible that the 
1 Pp. 202-256. 2 p. 283. 
3 ‘ Pro. Amcr. Phil. Soc.,’ vol. XVII., p. 225, 1S77 : this species is said to be allied to M. lohgiroslris. 
4 ‘ Pep. U.S. Geol. Surv.,’ 1873, p. 531 : this species is known only by one perfect tooth, and some broken teeth, and an 
astragalus : it is not stated whether it is a Tetra- or Trilophodon. 
3 ‘ Phil. Trans.,’ 1882, p. 772. 
6 The present writer is fain to confess that he can see no reason for assigning the tusk in question to a new genus. 
7 M. latidens ranges into Sind ; in Dera Bugti and the Biigti Hills no remains of tetralophodons have been found. 
E 
