446 



HISTORICAL GEOLOGY 



limestones. Where these flowerlike animals were abundant on the 

 sea bottom, they must have presented an appearance not unlike that 



Fig. 415. — Silurian crinoids : A, Eucalyptocrinus elrodi; C, Eucalyptocrinus crassus 

 (closed). Cystoid : B, Caryocrinus ornatus. Blastoid : D, Troostocrinus reinwardti. 



of a field of lilies. Not only did they live in great numbers, but the 

 variety of forms which were developed was large. 



Cystoids (Fig. 415$) 

 continued to be abun- 

 dant when conditions 

 were favorable for 

 their growth, but at 

 the close of the period 

 they were no longer an 

 important element of 

 ^tv^ WL the fauna. 



Molluscoidea 



Brachiopods. — Al- 

 though the Silurian 



brachiopods (Fig. 416 

 PIO, 416. — Silurian brachiopods: //, Rhynochotreta \ j 1 



■uana; H, Spirifcr radiatus ; C, Strcptis A-D) differed almost 



entirely from those of 



D t Ptntamerus oblongus. 



