4 THE VOYAGE OF H.M.S. CHALLENGER. 



yoiiuger animal C, from the Falkland Islands, was also, after a careful comparison with 

 the adult skull, regarded as an immature example of the same Mesojolodon, and not as a 

 new species. For although it diifered from the adult in some important characters, such 

 as the absence of a mesorostral bone, and of a maxillary buttress, whilst the teeth were 

 embedded in their sockets, yet these are differences which are perfectly explicable on the 

 ground of the immaturity of the specimen, which may have been, perhaps, also of the 

 female sex. That the specimen was immature, was satisfactorily shown by the open 

 condition of the cranial sutures, the lightness, porosity, and indeed fragility of the cranial 

 bones, and the non- ossification with the vertebral bodies of their plate-like epiphyses. I 

 may also mention that my friend Professor Flower, who has also examined the skull, 

 coincided in the opinion that it was an immature Mesoplodon layardi. 



As the characters of the skull of the adult Mesoplodon layardi have been described 

 with more or less fulness of detail by one or other of the naturalists already referred to, it 

 seems unnecessary that I should give a detailed description of specimen A. But as no 

 account has yet appeared of so immature a skull as that from the Falkland Islands, it is 

 advisable that it should be described, and the most satisfactory way of recording its 

 characters wiU be to write a comparative account of the younger and adult crania. In 

 the course of this description I shall pursue almost the same order as that observed in 

 the account which I gave a few years ago of the skull of Mesoplodon soiverhyi^ so 

 that a ready comparison between the crania of Layard's and Sowerby's whales may be 

 instituted. 



In the first place I append a table of the dimensions, expressed in inches, of the crania 

 of these specimens, and along with them I include the measurements of the skull of 

 Ziphius cavirostris. The dimensions are taken between the points adopted by Professor 

 Flower in his Memoir on the genus Mesopilodon,^ so that a comparison may be made 

 between these crania and the species Mesoplodon australis, grayi, and hectori, described 

 by him. 



1 Trans. Roy. Soo. Edin., May 20, 1872, vol. xxvi. 



2 Trans. Zool. Soc. 1877, vol. x. 



