SIWALIK AND NAEBADA BUNODONT SUINA. 
47—13 
Vertebrce mid limi-bones . — Two vertebrae and several limb-bones of Narbada 
liipj)opotami are figured in the “ F.A.S.” under the name of H. palaindicus ; but it is 
quite impossible to say whether they belong to that species or to II. namadicus. A 
very large collection of similar bones from the Narbadas is contained in the Indian 
Museum, but has never been described. The femuE has a larger great trochanter 
and a more prominent head than in II. amphihius^ and the shaft of the bone is 
apparently longer and more slender. 
Distribution . — Like II. namadicus., this species is only certainly known from the 
Narbadas ; but it probably also occurs in the corresponding deposits of the other 
large rivers. The association of hippopotamus remains with stone implements in 
the Narbadas ^^roves the coexistence of man in India with these animals, and hence 
Falconer’s conjecture that the so-called ^water-elephant’ of the early writings of 
India refers to a tradition of the existence of that animal may not improbably be 
correct.^ 
General Remarks on the genus Hippopotamus. 
Generic unitij of hexa- and tetraprotodont forms. — The case of H. palceindicus., which 
in its lower jaw is really a Ilexaprotodon in process of conversion into a Tetraprotodon, 
coupled with the instance of unilateral hexaprotodontism in II. ampMhius^^ indicates 
that Falconer’s two subgenera should be abolished. This point being admitted there 
are but slight grounds for retaining the subgenus, or genus, Olimropsis ; and 
accordingly all the species of hippopotamus may be referred to a single genus. 
Lines of specialization . — The Indian species of the genus indicate that the 
specialization of the genus has advanced on two main lines ; firstly., in the shortening 
and widening of the mandibular symphysis, frequently accompanied by a general 
shortening of the cranium and mandible ; and, secondly, in the reduction of the 
number of incisors, this reduction probably occurring first in the lower jaw, and 
being accompanied by the largely increased size of one or more of the remaining 
pairs of teeth. These features are apparently also accompanied by an increase in 
the size of the canines. 
The most primitive form of mandible is exhibited by II. iravaticus, in which the 
long narrow symphysis, the six small incisors, and the small canines, indicate an 
animal much closer to the pig than any other species of which the mandible is 
known. The next step is II. sivalensis, in which the symphysis is considerably 
shorter, although the incisors still preserve their small size. The third step is II. 
namadicus, in which the symphysis has still more decreased in length, while 175 has 
become slightly smaller, and is thrown more or less above the line of the other two. 
The fourth step is exhibited by H. palccindicus, in which the symphysis is shorter 
than in any other form, while iTi and i. 3 have increased enormously in size at the 
expense of 172, which becomes wedged in between the other two. It is highly 
1 “ F.A.S. lA. LVIII. 2 “ Pal. Mem.,” vol. II., pp. 613-4. 3 Vide .supra, Z1 . 
