112 MR. W. H. FLOWER ON THE OSTEOLOGY OF 
these-may also be added Platanista and Inia. Here, then, is a character derived from a 
part of the organization apparently less liable to adaptive modification than the teeth or 
fins, which may be taken as the basis of a primary division. It must now be seen whe- 
ther the remaining essential structural modifications are in accordance with it. Still 
confining our attention to the axial skeleton, there are certain tolerably obvious pecu- 
liarities about the vertebral column, more especially in the thoracic region, that will 
afford considerable assistance. As before indicated (p. 98), a peculiar mode of attach- 
ment of the ribs to the vertebrz is constantly found associated with the sterno-costal 
bones. The genera thus characterized may therefore be separated at once as a distinct 
natural group. They have also several minor characters in common, which will be 
pointed out presently. 
Should the whole of the genera with cartilaginous sternal ribs be united into a single 
group, equivalent to that just marked off? I am inclined to think that they should 
not. To revert to the same point of structure just mentioned, it was shown before that 
Physeter and Hyperoodon agree in a very peculiar condition of thoracic vertebre and 
rib-attachments. Whether Aogia and the Ziphioids conform with their nearest allies 
in this respect I am not at present able to say; but we may assume with tolerable 
certainty that they do. But here, as well as in many more trivial characters, including 
the teeth and pectoral limbs, /nia and Platanista differ—and differ, as it appears to me, 
more than any of the true Dolphins do, inter se. I would therefore raise the Cacha- 
lots and Ziphioids on the one hand, and Platanista and Jnia on thee other, to the rank 
of primary divisions of the Toothed Whales. With the latter it is in the highest degree 
probable that the genus Pontoporia should be associated. This group is not so com- 
pact and easily defined by positive characters as the other two, between which it 
naturally stands. The two genera whose structure is most completely known vary 
widely from each other, one diverging towards the Physeteride, the other towards the 
Delphinide, yet distinctly marked off from either. The validity of the group as a 
natural one will be greatly strengthened if the skeleton of Pontoporia should be found 
to possess the characters common to Platanista and Jnia*. It would be interesting, 
moreover, if it should be discovered that this Dolphin is, like the members of the other 
two genera, habitually fluviatile. 
* Dr. Gray in the “Zoology of the Voyage of the Erebus and Terror” placed Jnia and Pontoporia in one 
section at the end of the family Delphinide, following immediately upon Platanista. In his recently published 
Catalogue, Platanista constitutes the fourth family (Platanistide) of the Cetacea, following the Catodontide ; 
Inia forms a separate (the fifth) family, Iniide ; and Pontoporia commences the sixth family (Delphinide), 
comprising all the remaining Dolphins except the Globiocephalide and the Ziphiide. 
Gervais (Hist. Nat. des Mammiféres, 1855) unites Platanista, Inia, and Stenodelphis (Pontoporia) to form 
one of the five tribes (Platanistins, Delphinins, Orcins, Monodontins, and Phocénins) into which the family 
Delphinidés is divided. The primary divisions of the order or families are :—Physeteridés, Ziphiidés, Delphinidés, 
and Balénidés. 
+ It is to be hoped that Dr. Burmeister may be able to obtain information on this point. I should mention 
