PLATANISTA. 497 



although no one could hesitate to separate it as a distinct genus and to regard it 

 as probably not far removed from Inia, he considered that the two could hardly 

 be placed under one common group, the JPlatanistina, under which Gray brought 

 together the genera JPlatanista, Inia and Fontoporia, and which genera he has 

 more recently^ elevated into as many families. 



The osteological features, however, of Inia were very imperfectly known 

 when Eschricht wrote, but now through the labours of Plower^ the structure of its 

 skeleton has been well ascertained. Professor Gervais^ in 1855 grouped Flatanista, 

 Inia and Tontoporia to form one of the five tribes {Flatanistins), into which he 

 divided the DelphinidcBy the last but one of his four primary divisions of the 

 Cetacea.* 



Professor Plower has pointed out that Inia, Tontoporia and Tlatanista agree in 

 the great development of the temporal fossa, which, however, is most marked in 

 Flatanista, and in this striking feature of the skull the last differs from all the other 

 dolphins. In Flatanista and Fontoporia the zygomatic process of the temporal 

 abuts against the back of the orbital process of the frontal, so that there is no post- 

 orbital process, but in Inia this process is separated from the post-orbital process 

 therein developed by a considerable interval. In all of these forms the zygomatic 

 process of the temporal has a great family likeness, and is distinguished from the 

 corresponding processes in other dolphins by its markedly stronger character, which 

 relates to the great development of the temporal fossa. In the skull of Flatanista 

 which formed the subject of Professor Plower's observations, he mentions that it 

 differed from that of Inia in the construction of the temporal fossa, namely, in this, 

 that the frontal and squamous were not separated from each other by the pointed 

 extremity of that portion of the parietal which forms the side of the fossa, whereas 

 in Inia the squamosal was shut off from articulating with the frontal, and in 

 Fontoporia the parietal prevents the union of the frontal and squamosal, and the 

 pterygoid articulates with all of these bones. In Flatanista, however, there would 

 appear to be considerable individual diversity as to the extent to which the pterygoids 

 separate the squamous from the frontal, which is certainly occasionally the case in the 

 skulls which have come under my observation, although the arrangement described 

 by Professor Plower is what is generally present. This variation is so modified in 

 different individuals that it cannot be ascribed to any other cause than an inherent 

 tendency in these bones slightly to alter their forms. 



Professor Plower has supplemented Eschricht's observations on the construc- 

 tion of the hard palate and has proved the correctness of the latter' s suggestion that 

 the palatine would be found in the nasal tube, and that the bones appearing exter- 

 nally on the palate and entering into the temporal fossa were the pterygoids, and 

 in these features Flatanista is unique among the Cetacea. Inia itself, which 



1 Oat. Seals and Wliales, B. M., p. 87, et seq. 



2 Trans. Zool. Soc, 1869, vol. vi. 



3 Hist. Nat. des Mammif., 1855, p. 321. 



It is a subject of regret to me that I have not had the privilege to consult the 13 Livr. of Van Benedeu and 

 Gervais' splendid work ' Osteographie des Cetaces.' 



p 3 



