THE EOCENE PERIOD. 305 



In the order of the Dibranchiates, we have a like phenomenon 

 to observe in the total extinction of the great family of the 

 " Belemnites. " No form referable to this group has hitherto 

 been found in any Tertiary stratum ; but the internal skeletons 

 of Cuttle-fishes (such as Belosepia) are not unknown. 



Remains of Fishes are very abundant in strata of Eocene 

 age, especially in certain localities. The most famous depot 

 for the fossil fishes of this period is the limestone of Monte 

 Bolca, near Verona, which is interstratified with beds of vol- 

 canic ashes, the whole being referable to the Middle Eocene. 

 The fishes here seem to have been suddenly destroyed by a 

 volcanic eruption, and are found in vast numbers. Agassiz 



Fig. 223. Rhombus minimus, a small fossil Turbot from the Eocene Tertiary, 

 Monte Bolca. 



has described over one hundred and thirty species of Fishes 

 from this locality, belonging to seventy-seven genera. All 

 the species are extinct ; but about one-half of the genera are 

 represented by living forms. The great majority of the 

 Eocene Fishes belong to the order of the " Bony Fishes " 

 (Teleosteans), so that in the main the forms of Fishes charac- 

 terizing the Eocene are similar to those which predominate 

 in existing seas. In addition to the above, a few Ganoids and 

 a large number of Placoids are known to occur in the Eocene 

 rocks. Amongst the latter are found numerous teeth of true 

 Sharks, such as Otodus (fig. 224) and Carcharodon. The 

 pointed and serrated teeth of the latter sometimes attain a 

 20 



