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If I may be permitted to express my own opinion on a 

 subject of considerable difficulty, and which certainly admits 

 of much doubt — although the difficulty proceeds entirely from 

 the paucity of species known, — I confess that I think the 

 affinities of carnivorous Cetacea among themselves would be 

 still better expressed by placing all the living species that 

 are known in the two following groups : Balcenidce and Del- 

 phinidce. We may then make the sperm whales — animals, 

 which, as we have shown, diffigr in no important particular 

 from dolphins — fall into the series of Delphinidce. 



But in order to understand this matter more clearly, we had 

 better consider the place which the order of Cetacea holds 

 in the class of Mammalia, This order is distinguished neatly 

 from all other mammals by the absence of hinder feet j and 

 the typical Cetacea are evidently those, which, in other 

 respects differ the most in structure from the other orders of 

 Mammalia. Now, one of the characters most prevalent in 

 these other orders is the possession of molar teeth implanted 

 in the maxillaries. Incisors ©r intermaxillary teeth are often 

 wanting, but, except in a few Edentata, which are destitute 

 of all teeth, the maxillary bones are always provided with 

 molars. Let us ask ourselves, then, what Cetacea are least 

 oceanic in general structure, and, at the same time, in the 

 possession of molars? The answer at once will be^ the 

 herbivorous group. The existing herbivorous Cetacea, 

 together with the extinct genus Zeuglodon, and perhaps 

 another fossil genus, form, without doubt, the aberrant group 

 of the order, and are all distinguished by the possession of 

 molar teeth with double roots, as distinct from their incisors. 

 The remaining Cetacea, forming the normal group of the 

 order, have no such molar teeth. ^ These may be divided into 

 1st, true whales, Balcenidce, or those Cetacea which have no 

 teeth, but more or less baleen instead : and, 2ndly, dolphins, 

 or Delphinidce, which have only conical teeth with single 

 roots, and more or less hollow, like those of crocodiles. 

 Now, this last group, or the family Delphinidce, may be 

 divided into sub-families, as foUows; the genus Inia of 



