ECHINODERMATA 487 



great importance. Each successive plant-bearing horizon of the 

 Cretaceous is characterized by its own special assemblage of plants, 

 but in its general features the Upper Cretaceous flora is essentially 

 modern. Cretaceous animals are sufficiently different from those 

 of the Jura, but the change is not so revolutionary as we have 

 found among the plants. 



FIG. 161. — Cinnamomum affine, 1/2. Laramie stage. (Lesquereux.) 



Foraminifera play an important part in the construction of Creta- 

 ceous rocks, especially of the great masses of chalk, while the green 

 sands are casts of foraminiferal shells in glauconite. The most 

 abundant genus, as in the recent Atlantic oozes, is Globigerina. 



Spongida. — In the Cretaceous of Europe Sponges are more nu- 

 merous and varied than at any other time, but in North America 

 they are far less common. 



Coelenterata. — The Corals were very much as they are to-day 

 and require no special description. 



The Echinodermata undergo some very marked changes. The 

 Crinoids are much reduced since the Jurassic, and never again 

 assume their ancient importance ; characteristic Cretaceous genera 

 are the stemless Uintaciinus (PL X, Fig. 1) and Marsupites. The 

 Sea-urchins are incomparably more numerous in Europe than in 

 North America ; of the Regular forms may be mentioned Pseudo- 

 diadema (X, 2), Cidaris, and Salenia, and of the Irregular forms, 

 To x aster (X, 3), Holaster, Cassidulus, etc. 



