648 



THE WONDERS OF GEOLOGY. 



Lect. VI. 



crinoideans destitute of a stem, and these must have been 

 free animals, floating at liberty through the water, like the 

 recent Feather-stars. 



The number of ossicula in the skeleton of a single encri- 

 nite is computed at thirty thousand ; but in the more com- 

 plicated Pentacrinites they exceed one hundred and fifty 

 thousand, and in the plumose Encrinites must amount to 

 hundreds of thousands. The detached ossicula occur in 

 myriads in the Mountain limestone and Silurian rocks, 

 and the relics of one species alone forms thick beds of 



marble. 



1 2 3 4 5 



6 7 8 9 10 



Lign 145.— Stems of Encrtnites and Pentacrinites. 



Pig. 1. Screw, or Pulley-stone ; a cast in the hollow of an encrinital column. 

 2, 4. Articulating surfaces of different kinds of encrinital ossicula. 

 3' 5. Portions of encrinital steins, or Entrochi. 6, 8, 10. Stems of Pentacrinites. 

 7, 9. Separate ossicula of Pentacrinites. 



39. Encrinites and Pentacrinites. — The fossil re- 

 mains of Crinoidea consist of the ossicula of the column, 

 arms, and tentacula ; of the plates of the vase or receptacle ; 



