354 



graceful animals attached to the sea floor by flexible stalks 

 and provided with feathery arms or tentacles around the 

 mouth (p. 297). The mollusks (Figs. 365 

 and 367), and their companions the brachi- 

 opods (Figs. 366, 368, and 369), developed 

 steadily along the lines already defined in 

 earlier times, and be- 

 came constantly more 

 numerous. Clearly 

 preserved fishes appear 



FIG. 363. The chain { , ,, ~ 

 coral (Halysites), here for the first time > 



common in Silurian but as yet they are 



limestones. j , i j 



rare, and the considera- 

 tion of them may best be deferred until 

 the Devonian is discussed. They were 



extremely primitive 



types, unlike any that 



are now living. 



Life on the lands. 



The plants, which we 



ma y wel1 believe 

 clothed the Silurian 

 lands, are almost un- 

 known, doubtless for 

 the same reason that 

 has been suggested to 

 explain the similar ab- 

 sence of information 

 about the flora 1 of 

 earlier periods : the 



FIG. 365. A stout 

 Silurian gastropod 

 (Strophostylus). 



FIG. 366Alarge and 



strongly beaked 



of marine origin. 



FIG. 364. A nearly 

 perfect crinoid, as 

 found in the Niagara 

 limestone of Indiana. 

 The roots served 

 merely for attach- 

 ment. 



brachiopod (Conchi- Equally scant is the 



dmm) of the Silurian " 



period. record of air-breathing arthropods, but 



1 The flora of a country or of a period is the entire assemblage of trees, 

 shrubs, herbs, and other plants living in that place or time. 



