THE DEVONIAN PERIOD 



457 



Corals are not equally abundant in all Devonian formations ; they 

 are rare in shales and sandstones, but are usually common in lime- 

 stones. This is not remarkable, since corals do not thrive in muddy 

 waters. 



Echinodermata 



Crinoids (Fig. 429 B) and starfish (Fig. 429 A) were much 

 more abundant than in previous periods, but cystoids were 

 rarer than in the Silurian. 



Blastoids (Greek, blastos, 

 bud) were locally abundant. 

 These echinoderms (Fig. 429 

 C), as the name implies, were 

 oval, with five petal-like divi- 

 sions resembling a flower 

 bud. They were armless 

 and were attached to the sea 

 bottom by a jointed stem. 

 Beginning in the Ordovician, 

 they culminated in the Mis- 

 sissippian (p. 480), after 

 which they occurred sparsely 

 and disappeared with the 

 Paleozoic. 



The starfish of Devonian 

 times had already acquired the habits of feeding which they possess 

 to-day. 1 



Molluscoidea and Mollusca 



Brachiopods (Fig. 430 A-P) were never more abundant in in- 

 dividuals and species than during portions of this period, and 

 many characteristic species were present. Long-hinged spirifers 

 were especially abundant and highly developed throughout the 

 Devonian. 



Bryozoans (Fig. 431 A-D) were locally abundant. 



Pelecypods (Fig. 432 A-E) flourished where the bottoms were 

 muddy and other conditions favorable. 



Gastropods (Fig. 433 A-C) were subordinate in numbers to the 

 pelecypods but were not uncommon. 



Fig. 429. — Devonian starfish, crinoid, and 

 blastoid : A, Palceaster eucharis; B, Melocrinus 

 milwaukeensis ; C, Nucleocrinus verneuili. 



1 Clarke, J. M., — Early Adaptation in the Feeding Habits of Starfish, 

 Philadelphia, Vol. 15, 1912, pp. 113-118. 



Acad. Nat. Sci. 



