GILL, PRIMARY SUBDIVISIONS OF THE CETACEANS. 121 



VIII. Synopsis of the Primary Subdivisions of the 

 Cetaceans. '.:> 



BY THEODORE GILL, M.A., M.D., Ph. D. 



THE interest that is now being manifested in the Cetaceans has in- 

 duced me to submit for publication, in advance of similar series for 

 all the mammals, the following series of dichotomous tables of the 

 subdivisions of the order, so far as the suborders, families, and sub- 

 families are concerned. In the compilation of these tables, I have not 

 only made use of all the material at my disposal, but have availed my- 

 self of all the publications on the order as a whole, as well as on its 

 various members. But more especially have I been indebted to the 

 various publications of Professor William Henry Flower, from whose 

 views I have rarely ventured or found cause to dissent. 



There are probably few, if any, modern naturalists who have seri- 

 ously studied the Cetaceans, who do not now consider those animals 

 to be most nearly related to the Carnivores, or Ferae. Between the 

 latter and the Cetaceans of the present age, the gap does indeed appear 

 to be very great, but it is bridged over, to a very considerable extent, 

 by the Zeuglodonts of the Tertiary epoch, and those forms so resemble 

 in some features the Pinnipeds, that the two groups have been com- 

 bined by more than one naturalist but notably by Giebel in the 

 same order. They may indeed be considered as derivatives from the 

 same original stock, and from the Zeuglodont stem have probably de- 

 scended, in different directions, the Toothed and Whalebone Whales. 

 While the former, in some features, such as the general form of the 

 skull, the teeth, etc., appear to deviate less from ordinary mammals, 

 the latter, in other respects, but especially in the development of the 

 olfactory organ and of the nasal bones, depart less than they from 

 the typical forms. It would therefore seem probable that the Denti- 

 cete have become differentiated as now recognized, little or not at all 

 in advance of the Mysticete, or in other words, that the latter are not 

 offshoots from the former, but both from one original stock. 



A list of the genera is appended to enable the reader to understand 

 the range of the groups, but no pretense to critical accuracy is made 

 in its behalf, some generic names being admitted for groups which are 

 scarcely of generic value, while other genera, based on extinct species, 

 are omitted, chiefly on account of the doubts relative to their rela- 

 tions. 



COMMUNICATIONS ESSEX INSTITUTE, VOL. VI. 16 March, 1871. 



