Dr. J. E. Gray on Seals. 343 



and stmcturc of fur or feathers, and otlicr external characters, 

 that occur during tlic growth of animals, and the differences 

 that take place in the outer appearance of the same animals in 

 the different seasons. Now that so much attention is paid to 

 the characters afforded by the skull, teeth, and other parts of 

 the skeleton to distinguish the recent species, and to separate 

 them from the allied animals Avhose remains are fomid in a fossil 

 state, it becomes most important that great attention should 

 be paid to the variation which takes place in the form of the 

 different bones during the progress of the animals towards ma- 

 turity or old age, and the variation that occm-s in the different 

 bones of the skeleton of the same species, or in the skeletons 

 of allied species. 



Having the importance of this study always before my eyes, 

 I send you an account of a difference which I have recently 

 observed in the form of the lower jaws of Seals during the 

 growth of the animals. 



The British Museum has lately received the skulls and 

 skeletons of some large European Seals (I believe, from the 

 Baltic) which were exhibited in the Zoological Gardens as the 

 " Ringed Seal, PJioca annellata.'''' They are very interesting 

 as showing the difference in the forai of the front part of the 

 lower edge of the lower jaw which occui's during the growth 

 of these animals. 



Unfortunately almost all the skulls of the European Seals 

 previously in the Museum collection are from young animals. 

 The examination and comparison of these skulls of yoimg 

 animals, and the comparison of these with the skulls of the 

 adult Seals received from Mr. Wood from Vancouver's Island, 

 which I described under the name of Halicyon Etc/mrdii, in- 

 duced me to believe that the form of the lower edge of the 

 " lower jaw afforded very good characters for the distinction 

 of the species." (See Proc. Zool. Soc. 1864, p. 30, and Cat. of 

 Seals and Whales in the Brit. Mus. 1865, p. 30.) 



The skulls of older specimens of Callocephalus vitulinus 

 in the British Museum show that, though the strength and 

 general form of the lower jaw, and especially the position of 

 the angle in the lower edge as compared with the condyle, 

 do afford good specific and even generic characters, the 

 form of the inner side of the lower edge, on which I have been 

 inclined to place reliance, varies considerably according to the 

 age of the specimens. In the young specimen, for example, 

 the inner edge of the front of the lower jaw is dilated and pro- 

 duced inwards, so as to form a protection to the front of the 

 gullet ; but as the animal increases in age, this dilatation 



