450 MESOZOIC TIME. 



Sow., Maclra rostrata ; Natica elegans Sow. ; Ammonites gigantem Sow. ; Ilybodus 

 strictw Ag. ; Cetiosaurus longus Owen. 



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

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

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

 chaoniscus Brodiei (an Isopocl 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 Mantelli 

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



Figs. 820, 821. 



Mollusks. — Fig. 320, Uuio Taldensis; 821 Viviparus (Paludina) fluviorum. 



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

 Cyrena, Planorbis, Limnaa, Unio, and Paludina. Fig. 820, Unio Taldensis Mant. ; 821. 

 Viviparus {Paludina) fluviorum Sow., also Melania attenuata Sow., Neritina Fittoni 

 Mant. 



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

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

 Eemipters, and Dipters, 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 Mantelli Ag., Hybodus sub- 

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

 Dinosaurs, of the genera Iguanodon, Hylteosaurus, Megalosaurus, Regnosaunis ; Fig. 814, 

 tootb. of the Iguanodon ; Crocodilians with biconcave vertebra?, of the genera Suchosaurus 

 Ganiopholis, Pacilopleuron, etc. ; with convexo-concave vertebra?, of the genus Cetiosaurus, 

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

 Crocodilus ; Pterodactyls; Turtles, as the Tretostemum punctatum Owen (Trionyx 

 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, Hayden & 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 



