108 MR. W. H. FLOWER ON THE OSTEOLOGY OF 



below. The alisphenoid is concealed by a plate of the pterygoid, which articulates with 

 all three bones just mentioned. 



The orbit is slightly larger in proportion to the length of the cranium than in Inia, 

 and therefore considerably more so than in Platanista. The upper margin forms a 

 wider arch than in the former; the postorbital process is broader and shorter; the 

 antorbital tuberosity much smaller, but still chietly formed by the malar bone. The 

 styliform processes are unfortunately broken off. 



The upper surface of the skull is remarkably flat, showing scarcely a trace of the 

 postnarial elevation. On this surface the frontal bones appear in a narrow, slightly 

 raised median piece behind the nasal bones, -7" long, and -5" wide, bounded laterally 

 by the posterior extensions of the maxiUaries — and on each side in the supraorbital 

 plates, of which a much broader piece is left uncovered by the maxiUaries than in 

 Inia. The nasals are flattened, ii-regularly quadrate plates, as in Inia, but, in con- 

 sequence of the direction of the frontals, lying nearly horizontally instead of vertically. 



The narial aperture is broader, but shorter, than in Inia, being encroached upon by 

 the largely developed antenarial tuberosities of the premaxillaries, which are broader and 

 flatter on the surface than in Inia. The upper obtusely pointed ends of the pre- 

 maxillaries extend to a level with the mferior border of the nasals, but do not arti- 

 culate with them, as a strip of the maxillary comes between. The hinder ends of 

 the maxiUaries are broader and flatter than in Inia ; but in front of the nostrUs they 

 are much more contracted, and above the orbits have, a smaU but distinct longitudinal 

 crest, -3" high at the middle and graduaUy subsiding at the ends. This is not a mere 

 elevation of the edge of the bone, as in Inia, but a distinct ridge placed some way within 

 the suture between the maxiUary and the orbital plate of the frontal, and of which there 

 is no trace in Inia. Between this crest and the elevated portion of the premaxUlary there 

 is a very deep and narrow fossa, continuous in front with an extremely narrow but deep 

 groove, which lies between the maxillary and premaxillary along the entire length of the 

 rostrum, and which is only faintly indicated in Inia. The rostrum is considerably 

 longer and narrower m proportion to the size of the cranium than in Inia. 



The palate-bones resemble those of Inia in not covering the vomer in the middle 

 line. They have a small free external plate. Unfortunately the greater part of the 

 pterygoids is broken away ; but enough remains to show that these bones do not conform 

 to the type of the ordinary Dolphins, but are arranged in a peculiar manner, apparently 

 intermediate between those of Inia and Platanista. A broad outer lamella, resembling 

 that so characteristic of Platanista, remains on each side, and, though not covering the 

 palatine anteriorly as in that genus, passes upwards and outwards to the temporal 

 fossa, overlying the alisphenoid and articulating with the squamosal, parietal, and 

 frontal 



The petrotympanic bones are wanting on both sides, showing that their mode of 

 attachment resembles that of Ma rather than that of Platanista. 



