146 A BOOK OR WHALES, 



genera were accepted by Flower in his paper on 

 " The Skeletons of Whales in the principal Museums 

 of Holland and Belgium" (in Proc. Zool. Soc. already 

 referred to). If we add to these Cuvieriiis for the 

 fourth species, described in the present work as Balcen- 

 optera sibbaldii, we shall have exhausted the possible 

 generic names for the only four species known. 



But are they wanted? It seems to be a reason- 

 able procedure in zoological nomenclature to invent 

 generic names for the clue pigeon-holing of a group 

 which embraces a large number of species. It 

 facilitates memory, and expresses a notion of classi- 

 fication. But when a group is so restricted as is 

 that of the Rorquals, this procedure seems to be 

 superfluous, especially since the utmost differences 

 between the recognised forms are so small. All 

 these great creatures are so much alike that their 



o 



confusion one with another is almost inextricable. 

 When species has been so confounded and confused 

 with species, it seems to be a deliberate sarcasm to 

 attempt generic definitions. Besides, now that the 

 group has emerged from the complexity in which 

 the labours of Dr. Gray involved it, we are able to 

 see clearly how slight are the anatomical differences 

 which distinguish the different forms. 



We think, therefore, that the best plan will be to 

 oqve some sketch of the external characters and 



o 



osteology of the Rorquals, and to mention the 

 differences which enable the different forms to be 

 distinguished from each other. 



The number of vertebrae differs, and the follow- 



