JNIA GEOFPRENSIS AJSTD PONTOPORIA BLAINVILLII. 91 



shutting off the squamosal from the frontal ; whereas in Platanista the last-named 

 bones unite for a considerable distance below the pointed anterior end of the somewhat 

 triangular parietal, and the alisphenoid does not appear in the fossa at all. 



The orbit, in its structure, as well as its size, is intermediate between that of Pla- 

 tanista and Beljihhms. Its antero-posterior diameter is 1". The malar bone is shorter 

 and more thick and tuberous than in the Dolphins generally, and contributes chiefly to 

 the formation of the prominent rounded antorbital eminence. The ends of the styli- 

 form processes are unfortunately broken off; but the portions that remain adhere to 

 the form prevalent among the Belphinidm. In the larger skull in the British Museum 

 this process on one side is 1" long, and appears to have a free, natural, rounded termi- 

 nation, not uniting, by .a very considerable interval, with the zygomatic process of the 

 squamosal. If this is constantly the case, Inia presents, in this respect, a remarkable 

 exception to all other Dolphins. There is no distinct lachrymal bone. 



The upper surface of the facial portion of the skull behind the rostrum is longer 

 and narrower than in the Belphinidm generally. It is distinctly bounded on each side 

 by the sharp, straight, and nearly parallel crest before spoken of as forming the upper 

 margin of the temporal fossa. Within these crests, on each side, the narrow upward 

 prolongations of the maxillaries are deeply hollowed. Their hinder edge extends an 

 inch further back than the anterior apex of the supraoccipital, and they curve inwards 

 round the top of the premaxillaries to articulate with the nasals, and enter for a small 

 space, between these bones and the premaxillaries, into the formation of the lateral 

 boundaries of the narial opening. It is the narrowness and excavation, combined with 

 the straightness and elevation of the outer borders, of the maxillariea, which gives 

 the peculiar character to the upper surface of the skull of Inia as compared with that of 

 Delpliinus. The difference is only one of arrangement of the same parts ; there is 

 nothing superadded like the extraordinary outgrowths upon the maxillae of Platanista. 



Immediately behind the narial opening is a somewhat square-shaped elevation, rising 

 vertically in front, sloping behind, and hollowed out and overhanging at the sides, 

 formed chiefly of the frontal bones, and suggestive of the peculiar elevation of this 

 ^part so characteristic of the Ziphioids. The nasal bones are applied to the front wall of 

 this elevation, but do not reach the top of it. In general form they are irregularly 

 quadrilateral, prominent and thick near their longest, straight, inner border, where 

 they meet each other in the middle line, and deeply hoUowed and notched in their 

 upper and lower margins. Their shorter, but straight and thick, outer border articulates 

 with the maxillary. Above and below they are bounded by the frontal, on which they 

 rest. The greatest length of each bone is -9", the greatest breadth -7". They present 

 no marked deviation from bilateral symmetry. Attached to the upper outer angle of 

 each, and lodged in the groove between the frontal and maxillary, is a minute oval 

 bone, -25" long, apparently originally distinct, though now partially united with the 

 nasal ; and their inferior internal angles rest upon a median single triangular piece, -3" 



