490 THE CRETACEOUS PERIOD 



minal chamber. Scaphites (X, 13) is like a shortened A ncyloceras. 

 In Ptychoceras (X, 12) the shell consists of two parallel parts, 

 connected by a single sharp bend. Turrilites is coiled into a high 

 spiral, like a Gastropod, and Baculites (X, 14) has a perfectly 

 straight shell except for a minute coil at one end. Nautilus is 

 represented by many species, some of them very large. Belem- 

 nites are very abundant, but in the Upper Cretaceous the genus 

 Belemnitella (X, 15) replaces the true Be km nites. 



The Vertebrata form the most characteristic element of the 

 Cretaceous fauna. Among the Fishes a revolution has occurred. 

 Sharks of modern type abound, and their teeth are found in count- 

 less numbers ; but the principal change consists in the immense 

 expansion of the Teleosts or Bony Fishes, which now take the 

 dominant place, while Ganoids become rare. Most of the Creta- 

 ceous Teleosts belong to modern families and even genera, such 

 as the Herrings, Cod, Salmon, Mullets, Catfishes, etc. ; but a 

 characteristic Cretaceous type, now extinct, is that of the Sauro- 

 donts, fierce, carnivorous fishes of great size and power. The 

 genus Portheus, common in the Kansas chalk, was 12 to 15 feet 

 long, and was provided with great, reptile-like teeth. 



. The Reptiles continued to be the dominant types of the land, 

 the sea, and the air, and it may fairly be questioned whether the 



Fig. 162. — Clidastes velox, 1/96. (Williston.) 



Jura or the Cretaceous should be regarded as the culminating 

 period of Reptilian history. Ichthyosaurs and Plesiosaurs are 

 perhaps less abundant than in the Jura, but are of greatly in- 

 creased size. Elasmosaurics, a Plesiosaur from the Kansas chalk, 

 had a length of 40 to 50 feet, of which 22 feet belonged to the 

 slender neck. Confined to the Cretaceous are the remarkable 

 marine reptiles of the group Pythonomoipha, or Mosasauria, which 

 swarmed on the Atlantic and Gulf coasts, and especially in the 



