INIA GEOFFRENSIS AND PONTOPORIA BLAINVILLII. 109 
The mandible resembles that of both Jnia and Platanista, and is intermediate 
between the two in narrowness and comparative length of the symphysis. Its osseous 
substance is very dense, and the two rami are completely ankylosed at the symphysis. 
Running along each side of the symphysial portion is a deep and narrow groove, corre- 
sponding to that on the rostrum between the maxillary and premaxillary. 
The teeth are implanted in distinct alveoli. As many have been lost from the 
anterior part of the lower jaw during life, and the sockets completely filled up, their 
number cannot be estimated with perfect accuracy, but it may be estimated as follows: 
57—56 
sap? All have broad fangs, much compressed laterally, surmounted by a 
crown, the base of which, when seen from aboye, is of a quadrilateral form, with the 
angles rounded off, longer from before backwards than from side to side; this suddenly 
contracts into a slender subconical apical portion, much compressed in the opposite 
direction, and slightly incurved at the apex, which is worn off in nearly all the teeth of 
this old specimen. ‘The enlarged base of the crown, which forms a sort of cingulum, is 
slightly granulated on the surface, and in the natural state is entirely concealed within 
the gum. ‘The projecting contracted portion has a smooth glossy surface. The teeth 
vary but little in size or form throughout the whole series of both jaws. The dimen- 
sions of one taken from the middle of the lower jaw are :— 
MENA an ES Alc gd, sncls- abode bag dap ageutisapase ounce ‘15 
TEE REO GROW coca sainag ~a0kb - ish «nines aah <bar ge daneavenest "24 
Antero-posterior breadth of cingulum .................. 7 
Transverse breadth of cingulum..................csseeeees ‘ll 
Antero-posterior breadth of apical part at middle ... 05 
PANS VEESGIO MCAD HDS «pm tere cides -spaiihdo«Espciciencieipiiesien' ‘10 
This peculiar form of the teeth, which distinguishes Pontoporia from all the ordinary 
Dolphins, and affords another evidence of its affinity with Jnia, has not been observed 
in the Paris specimen. Gervais’s description is as follows:—‘ Les dents * * * * sont 
petites, longues de 5 ou 6 millimetres au plus, toutes plus ou moins aigués, et au 
nombre de 53 ou 54 supérieurement, ainsi quinférieurement. Les postérieures sont un 
peu moins aigués que les autres, et leur partie terminale est un peu recourbée.” 
The Paris skull, moreover, according to the figures, has a less elongated and slender 
rostrum than the present specimen—a difference which may certainly depend on age, 
presuming that the two animals belong to the same species. 
- IIL. On the Systematic Position of Inia and Pontoporia in the order Cetacea. 
_ The foregoing sketch of the principal osteological features of Inia shows that this 
Cetacean presents peculiarities sufficient to constitute it a well-marked genus among 
the Dolphins, Its natural position in the order, and its affinities, however, can only be 
