CHAP. X.] 



CONTINUITY OF THE CHALK. 



and he referred the group to the Polyzoa. When 

 Mr. Toulmin Smith studied the Ventriculites, the 

 Hexactinellidae the sponges with six-rayed meshes 

 or spicules were practically unknown, though there 



FIG. 80. J'rntricuUtes siinpk.i; TOCLMIN SMITH. Once and a half the natural si/t-. 



were already a few examples in museums. One of the 

 first results of deep-sea dredging was the discovery 

 that the chalk-mud of the deep sea is in many places 

 literally crowded with these ; and when we compare 



i T 2 



