INIA GEOFFRENSIS AND 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 Delphinus. 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 Delphinide. 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, Zvia 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 Delphinide 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 maxillaries, which gives 
the peculiar character to the upper surface of the skull of /néa as compared with that of 
Delphinus. The difference is only one of arrangement of the same parts; there is 
nothing superadded like the extraordinary outgrowths upon the maxille 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 hollowed 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'' 
