ENCRINITES. 



119 



that we sometimes find nothing else? "Screw- 

 stones," the country folk call some of them that 

 name being given in reality to those siliceous casts 

 of encrinital stems which occur abundantly in the 



Fig. 98. Platycrinus tri- 

 gintidactylus (Carboni- 

 ferous limestone). 



Fig. 97- Glyptocririus (Silurian). 



Fig. 99. Head of Actinocrinus 

 cusfidatus (Carboniferous 

 limestone). 



chert-bands, where the original limy matter of the 

 ossicles (or individual joints of the stems) has been 

 dissolved away, leaving only thin plates of flinty 



