134 



HISTORICAL GEOLOGY 



the Chain Corals having become rare and extinct in the early 

 Devonian. The solitary Cup Corals probably reached their culmi- 

 nation in size, some of them being 12 to 18 inches long and several 

 inches in diameter. 



Echinoderms. — Cystoids were rare and became extinct during 

 this period. Blastoids still continued to assume a minor role. 



Fig. 73 



A Devonian Asterozoan, Paleaster eucharis, on a Pelecj-pod shell. 



(After Clarke, N. Y. State Mus. Bui. 158.) 



Crinoids continued to increase and diversify. Asterozoans (Star- 

 fishes) notably increased (Fig. 73), while the Echinozoans (e.g. 

 Sea-urchins) were only moderately represented. 



Molluscoids. — Bryozoans were present, but not conspicuous 

 as reef builders. 



Brachiopods reached their culmination as regards numbers of 

 species and abundance (Fig. 74). Here, as in the three preceding 

 periods, Brachiopods were the most numerous fossils, and most 



