450 



MESOZOIC TIME. 



Sow., Mactra rostrata ; Natica elegans Sow. ; Ammonites giganteus Sow. ; Hybodus 

 strictus Ag. ; Cetiosaurus longus Owen. 



7. Purbeck Beds. — Mantellia megalophylla Br. (Fig. 762); Hemicidaris Purbech- 

 ensis Forbes; Ostrea distortd Sow. ; Paludina carinifera Sow.; Cypris (various species); 

 Aspidorhynchus Fisheri Eg., Goniopholis crassidens Ow. (a Crocodilian); Fig. 800, Ar- 

 chceoniscus Brodiei (an Isopod Crustacean). Mammals, Plagiaulax Becklesii, P. minor, 

 Spalacotherium Brodiei Owen. 



3. Wealden Epoch. 



1. Plants. — Conifers closely allied to Araucaria, Abies, Cupressus, Juniperus; 

 Cycads ; trees allied to Dracaena, Yucca, and Bromelia ; Ferns, the Sphenopteris ManteUi 

 Brngt., Clathraria Lyellii Mant, etc.; the delicate Charce of rivulets. 



Figs. 820, 821. 



Molltjsks. — Eig. 820, Unio Valdensis; 821 Viviparus (Paludina) fluviorum. 



2. Mollusks. — Fresh-water species in large numbers, especially of the genera 



Cyrena, Planorbis, Limnwa, Unio, and Paludina. Fig. 820, Unio Valdensis Mant. ; 821. 

 Viviparus (Paludina) Jluviorum Sow., also Melania attenuata Sow., Neritina Fittoni 

 Mant. 



3. Articulates. — Ostracoids, related to Cypris, etc., very abundant in some 

 layers. Insects of thirty or forty families, including Coleopters, Orthopters, Neuropters, 

 Hemipters, and Bipters, or Beetles, Crickets, Dragon-flies, Cicadas, May-flies, etc. 



4. Vertebrates. — Fishes, of the orders of Ganoids and Selachians, in all thirty 

 or forty species, including Lepidotus Fittoni Ag., Pycnodus ManteUi Ag., Hybodus sub- 

 carinatus Ag. Reptiles. — Enaliosaurs, ot the genera, Ichthyosaurus and Plesiosaurus ; 

 Dinosaurs, of the genera Jguanodon, Hylceosaurus, Megalosaurus, Regnosaurus ; Fig. 814, 

 tooth of the Iguanodon ; Crocodilians with biconcave vertebras, of the genera Suchosaurus 

 Goniopholis, Pozcilopleuron, etc. ; with convexo-concave vertebras, of the genus Cetiosaurus, 

 and also the first of the concavo-convex, or procoelian, in species of the modern genus 

 Crocodilus; Pterodactyls; Turtles, as the Tretosternum punctatum Owen (Trionysn 

 Bakewelli Mantell), etc. 



3. General Observations. 



Geography. — From the outcropping of the Jurassic beds along the 

 Black Hills and the flanks of the Rocky Mountains, Hay den & Meek 

 have inferred with good reason that these rocks probably underlie the 

 wide-spread Cretaceous strata of the eastern slope of the Rocky 

 Mountains ; and, as the elevation of the Rocky chain above the ocean 

 was not completed until long after the close of the Cretaceous period 





