16 



HISTORICAL GEOLOGY 



Fig. 5 

 A group of modern Corals showing the internal structure of one individual. 

 (After Pfurtscheller, from Schuchert's "Historical Geology," permission 

 of John Wiley and Sons.) 



Among Pelmatozoans, the Cystoids are small, bladder-like forms 

 with irregular radial arrangement of plates of the shell and arms 



b c 



Fig. 6 

 Stemmed Echinoderms (Pelmatozoans). a, Cystoid, b, Blast oid, 

 c, Crinoid. 



