354 



HISTORICAL GEOLOGY. 



continue in great numbers, though they disappear at the 

 end of the Cretaceous ; but, in addition to the usual form, 

 the Ammonites take on now the most strange and un- 

 accountable shapes (Figs. 313-316). Some are partly 

 uncoiled, as in Scaphites (boat), Toxoceras (bow-horn), 

 Ancyloceras (curved-horn), Hamites (hook); in some, 

 completely uncoiled and straight, as Baculites (staff). 

 Sometimes they are coiled spirally, like a gasteropod, as 



Fio. 817. Cretaceous fishes Teleosts : Osmeroides Miintelli. 



in Turrulites. But for the complexity of the suture, no 

 one would imagine a baculite or a turrulite to belong to the 

 Ammonite family. It is probable 

 that rapidly changing and unfav- 

 orable conditions tend to produce 

 new and strange forms. The Am- 

 monite family were on the point 

 of becoming extinct. 



Fishes. Here we note another 

 great step in the progress of life. 

 The Teleost fishes, the vastly pre- 

 dominant kind at the present day, 

 are here first introduced, and al- 

 most immediately become abun- 

 dant. The Ganoids at once be- 

 come very subordinate. The 



sharks, however, are abundant and of large size, and of the 



highest kind, viz., Squalodonts, or true sharks (Fig. 318). 



Reptiles. If, in Europe, reptiles seem to have culmi- 



PIG. 318 Cretaceous fishes- 

 Sharks: Otodus. (After Leidy.) 



