INIA GEOFPEENSIS AJMD PONTOPOEIA BLAINVILLII. 109 



The mandible resembles that of both Inia and Flatanista, and is intermediate 

 between the tAvo 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 : 

 3jj^^|j-,=22i?. 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 ai-e : — 



Length of fang '15 



Length of crown '24 



Antero-posterior breadth of cingulum 47 



Transverse breadth of cingulum '11 



Antero-posterior breadth of apical part at middle ... '05 



Transverse breadth '10 



This peculiar form of the teeth, which distinguishes Fontoporia fi-om all the ordinary 

 Dolphins, and affords another evidence of its affinity with Inia, 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 aigues, et au 

 nombre de 53 ou 54 superieurement, ainsi quinferieurement. Les posterieures sont un 

 pen moins aigues que les autres, et leur partie terminale est un pen recourbee." 



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. 



- III. On the Systematic Position o/Inia and Pontoporiam 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 



