860 



HISTORICAL GEOLOGY. 



Animals. — 1. Rhizopods. — Foramiuifers are commonly the principal 



material of the Chalk. Ac- 

 1444-1447. cording to Ehrenberg, a cubic 



1444 1445 a 1446 1447 a ^^^^^ ^f ^^^i^ ^f^g^ contains 



more than a million of micro- 

 scopic organisms, which are 

 chiefly the shells of Ehizopods. 

 Some of the species are repre- 

 sented much enlarged in Figs. 

 1444-1447. 



Ehizopods. — Fig. 1444, Lituola nautiloidea ; 1445, a, Flabellina 

 rugosa ; 1446, Chrysalidlna gradata ; 144T, a, Cuneolina 

 pavonia. 



2. Sponges. — Sponges were 

 of like importance in the history of the Cretaceous rocks on account of 

 their siliceous spicules and framework, which were the chief source of the 

 flint. The recent discovery over the ocean's bottom of Sponges whose 

 fibers are wholly siliceous was a revelation as to their importance in 

 flint-making. The species are mostly of the Hexactinellid and Lithistid 



1448 



1448, 1449. 



1449 a 



1449 & 



Sponge. — Fig. 1448, Siphonia lobata. Echinoderm. — Figs. 1449 a, b, Ananchytes ovatus. 



kinds. One of the Lithistid kind is represented in Fig. 1448, and spicules 

 from various sponges in Figs. 446-460, on page 432, obtained by G. J. 

 Hinde, from a cavity in a mass of flint, which afforded also a multitude of 

 other forms. The Cretaceous Hexactinellids comprised the goblet-shaped 

 Ventriculites, and many other kinds. 



3. Corals, Echinoids. — Corals and Echinoids were common in some of the 

 limestones, especially those of southern Europe. The Corals were of modern 

 type in being Hesacoralla ; and one Cretaceous genus, Caryophyllia, has still 

 its many species. 



Echinoderms were of many genera and species, especially in the Upper 

 Greensand (Cenomanian) and chalk. The Ananchytes ovatus, Fig. 1449, is of 

 the Upper Chalk (Senonian) of England. With it, and also in the Ceno- 

 manian, occur species of Holaster, Micraster, Salenia, Galerites, and others. 



4. Mollusks. — Lamellibranchs included many species of the genera Gry- 

 phcea, Exogyra, Inoceramus, Trigonia, which are rare after the Cretaceous, 

 or end with it, and also of Pecten, Lima, etc. They comprise also the pecul- 



