RECORD OF LIFE IN THE ROCKS. 175 



pulpy in their consistence, many of them, however, hav- 

 ing a hard frame-work, as the coral animals and the star- 

 fishes. They live to a great extent on the microscopic 

 organisms which abound in the sea; and, though they are 

 more zoological than the protozoans, they are largely ge- 

 ological, especially the coral animals, which have con- 

 tributed, and still contribute, as you have seen ( 236), 

 such quantities of limestone to the earth-making pro- 

 cesses. 



258. Mollusca. This class, Fig. 95, contains animals 



Fig. 95. 



of a much more complicated and varied character than 

 the preceding. They are not confined to the ocean, but 



