150 



OUR COMMON BRITISH FOSSILS. 



buried themselves in the chalky mud of the ancient 

 sea in a similar manner. Some of the modern Echini, 

 on the other hand, have the power of hollowing for 

 themselves holes in the rocks by the sea, especially in 



Fig. 122. — Ananchytes ovata, or "fairy loaf," a common Cretaceous Echinoderm : 

 a, base, showing position of mouth and anus. 



limestone rocks, which are not unfrequently found 

 riddled by them, just as they are by Pholas and other 



Fig. 123. — Natural flint cast of interior oi Ananchyte (very common in Norfolk and 

 Suffolk), showing the perforations (in relief) for ambulacral or sucking-feet. 



boring molluscs. A pretty little sea-urchin, not quite 

 so big as a threepenny piece, which we find not 

 uncommonly fossilized in the Red Crag beds, is the 



