PART II. CHAPTER XV. 



185 



Fossils of the Chalk. 



(see Figures,) which are alike marine. They are dispersed 

 indifferently through the soft chalk and the hard flint. 



Fig. 158. 



rfnanchytes ovatus. 



a. side view. 



b. bottom of the shell on which both the oral and anal apertures are placed ; 



the anal being to the right, and more oval. 



Fig. 159. 



Eschara disticha. 

 a. natural size. b. portion magnified. 



To some of these inclosed zoophytes many flints owe their 

 irregular forms, as in the flint represented in Fig. 161., where 

 the hollows on the exterior are caused by the branches of a 

 sponge, which is seen on breaking open the flint. (See Fig, 160.) 



Fig. 160. 



Fig. 161. 



A branching sponge in a flint from the chalk. 



