CRETACEOUS PERIOD. 473 



(fig. 788), from hamus, a hook; Toxoceras (fig. 789), from rogov, a bow; 

 Baculites (fig. 768), from baculum, a walking-stick. Turrilites (fig. 

 790) is another form, unlike other Ammonitids in being a turreted 

 spiral. Another genus resembles an opened spiral, and is called Heli- 

 coceras. Among these genera, only Ammonites, S'caphites, Ancyloceras, 

 Hamites, Ptychoceras, Baculites, Turrilites, and Helicoceras, have been 

 found in American Cretaceous rocks. Baculites ovatus (fig. 768) 

 attains a length of a foot or more, and a diameter of 2J inches, 

 and Scaphites Conradi (fig. 766) a length of six inches. Ancyloceras 

 and Toxoceras occur first in the European Jurassic. 



Among Vertebrates, there is the first appearance of several pro- 

 minent modern groups, marking grand steps of progress in the 

 life of the world. The most prominent is that of 



Common or Osseous Fishes, or Teliosts, — the tribe which includes 

 nearly all fishes, excepting Ganoids and Sharks, and, consequently, 

 nearly all edible species. Their distinguishing characteristics are 

 mentioned on page 278. 



Besides this mark of progress, there are many other new genera 

 of Fishes, and several of Eeptiles. 



The Squalodonts, or modern tribe of Sharks, having teeth with 

 sharp cutting edges besides other peculiarities, are greatly multi- 

 plied. The new tribes do not displace the Cestracionts and Ga- 

 noids, which continue to be common until the close of the Creta- 

 ceous period, and still have some representatives. 



Figs. 772, 773, represent some of the Sharks' teeth. Fig. 

 773 are pavement-teeth of a fish of the old Cestraciont group, 

 pertaining to the genus Ptychodus, characteristic of the Cretaceous 

 period. 



Beyond the Mississippi, remains of Reptiles have been found, 

 and both there and in New Jersey bones of a colossal Lacertian 

 Reptile of the genus Mosasaurus. These Reptiles are supposed to 

 have been web-footed and aquatic in habit, while at the same time 

 carnivorous. The tail was flattened, long, and powerful, and thus 

 fitted for sculling through the water. The New Jersey species was 

 24 feet long. Another large Reptile, Hadrosaurus Foulkii Leidy, is 

 related to the Iguanodon of the Wealden, and was probably 25 

 feet long ; its remains were found near Haddonfield, N.J. 



