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



which he regarded as a new genus, CaUidon, but which Mr Krefft, who obtained the 

 specimen, named Mesoplodon gimtheri, closely approximates, in the relation of the den- 

 ticle to the fang, to the tooth of the young Mesoj^lodon layardi descril^ed in this com- 

 munication. It differs, however, slightly in the shaj)e of the fang, which in the Little 

 Bay specimen is more elongated than in my specimen, so that the tooth is a little larger. 

 There is nothing, however, in this character to found specific, still less generic, distinc- 

 tion on, so that I am prepared to support Professor Flower's opinion that the Little Bay 

 cetacean is an example of Mesoplodon layardi. 



The Little Bay animal is said to have been 18 feet in length, which is also stated to 

 have been about the length of the specimen described by Dr von Haast. The animal 

 from which the adult teeth described in this communication were procured was said to 

 have been from 16 to 18 feet long, and both in it and in von Haast's specimen the teeth 

 had protruded, so as to form large tusks, whilst in the Little Bay example, and the one 

 from the Falkland Islands, which was certainly under 14 feet long, the teeth are rudi- 

 mentary in size. Now, as the Little Bay and von Haast's animals were of about equal 

 length, and as von Haast's specimen, with well-developed teeth, was determined to 

 be of the male sex, it is not unlikely that the little Bay and Falkland Island specimens 

 were females, so that the presence of well-developed tusks in the skull of Mesoplodon 

 layardi, and it may be in the other zi23hioid cetacea also, is probably a character of 

 the male sex. 



As I have had the opportunity of examining the structure of a tooth in a young 

 Mesoplodon soiverbyi, and as no account of the unprotruded tooth of this species has 

 yet been put on record, it may not be out of place to include a description of it in this 

 Report.^ The tooth was from the mandible of the skull, the characters of which I 

 described some years ago in the Transactions of the Royal Society of Edinburgh.^ In 

 many of its characters this tooth differed from that in the skull of the adult male 

 in the Oxford Museum, described by Professor E. Ray Lankester,^ which is probably 

 due to the difference in the age of the two specimens, and it may be to a difference 

 in sex. 



The two teeth of the young Mesoplodon sowerhyi were imbedded in their sockets, in 

 the lower jaw, out of which only the apex projected. Each tooth was laterally com- 

 pressed, and triangular in form. Its vertical diameter, from base to apex, was 2 inches, 

 its antero-posterior diameter, along the base, 2^th inches. The anterior border was 

 longer and more oblique than the posterior, so that the apex of the tooth was directed 

 upwards and backwards. There was no sharp demarcation into crown and fang ; although 



1 I gave an account of this tooth, and that of Mesoplodon layardi, to the Royal Society of Edinburgh on June 2, 

 1879, and printed it in the Journal of Anatomy and Physiology, July 1879. 



2 Vol. xxvi. 1872. 



^ Transactions of the Royal Microscopical Society, printed in Quarterly Journal of Microscopical Science, 

 vol. vii. 1867. 



