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



any evidence of having been rolled or rubbed. They had evidently rested quietly in the 

 spots where they had been deposited, and in many cases the tympanic and petrous bones 

 were still attached to each other, although they could be separated by the exercise of but 

 little force. 



The sharks' teeth belonged to the genera Carcharodon, Oxyrhina, and Lamna, and are 

 to be referred to no species, so far as we know, now living. They are identical with the 

 sharks found in the Tertiary deposits. The question, therefore, natu.rally arises. Are the 

 cetacean remains associated with them on the floor of the ocean the bones of existing or 

 extinct forms ? Of the resemblance of the greater number of these bones, more especially 

 the tympanic bullae, to existing genera, I have given a number of examples, and have 

 occasionally had to point out how closely some of them correspond with existing species, 

 so that they may be referred to them. But whilst these may be the bones of species still 

 extant, there are others which present greater difficulties in the identification, so that, 

 like the sharks, they may have belonged to animals which had lived in a previous geolo- 

 gical epoch. 



This observation will more especially apply to the undetermined bones found at the 

 various stations in the central southern portion of the South Pacific Ocean. In none of 

 these stations was the depth less than 14,000 feet, and in one (274) it reached 16,500 feet. 

 From the position of these stations in mid-ocean, its floor in them is subjected, as Mr 

 Murray has shown, to a minimum amount of deposition from above, so that but little 

 change can have taken place in the ocean bed in these localities during a great period of 

 time. The occurrence of the teeth of sharks, identical with known Tertiary species, lying 

 so loosely on the ocean floor that they can be scraped up by the dredge, may show 

 either that the sea bottom in these regions has remained unchanged, and with scarcely 

 any appreciable gain from deposition since Tertiary times, or that some species of shark 

 have continued to haunt these waters from the Tertiary down to the present period. In 

 the former case, which other data render not improbable, the remains preserved may 

 represent organisms existing during the Tertiary epoch, as well as animals which have 

 lived and died in the ocean from that time to the present. From the peculiar circum- 

 stances of the case, therefore, animal remains, belonging to periods of time widely remote 

 from each other, may be lying side by side in the same place on the sea bed, so that 

 the association together of their remains may not necessarily imply that they were 

 co-temporaneous, But if there has been, as seems not improbable in these very 

 deep localities in mid-ocean, no appreciable geographical change since the Tertiary epoch, 

 and if the food supply and the climatic conditions as regards ocean temj)erature have 

 remained uniform, one sees no good reason why animals which lived in these seas during 

 those remote times should not also be found there at the present day, if our knowledge of 

 the oceanic fauna were complete. It may be precipitate, therefore, to pronounce the 

 ear-bones, which we have not been able to refer to living sjDecies, to be those of extinct 



