THE LOWER AND UPPER SILURIAN AGES. 69 



articulated and capable of being flexed in any direc- 

 tion. Such a creature has more the aspect of a flower 

 than of an animal ; yet it is really an animal, and sub* 

 sists by collecting with its arms and drifting into its 

 mouth minute creatures floating in the water. Ano- 

 ther group, less typical, but abundantly represented in 

 the Silurian seas, is that of the Cystideans, in which 

 the body is sack-like, and the arms few and sometimes 

 attached to the body. They resemble the young or 

 larvaa of crinoids. In the modern seas the crinoids 

 are extremely few, though dredging in very deep 

 water has recently added to the number of known 

 species; but in the Silurian period they had their 

 birth, and attained to a number and perfection not 

 afterwards surpassed. Perhaps the stone-lilies of the 

 Upper Silurian rocks of Dudley, in England, are the 

 most beautiful of Palaeozoic animals. Judging from 

 the immense quantities of their remains in some lime- 

 stones, wide areas of the sea bottom must have been 

 crowded with their long stalks and flower-like bodies, 

 presenting vast submarine fields of these stony water- 

 lilies. 



Passing over many tribes of mollusks, continued or 

 extended from the Primordial and merely remarking 

 that the lamp -shells and the ordinary bivalve and 

 univalve shell-fishes are all represented largely, more 

 especially the former group, in the Silurian we come 

 to the highest of the Mollusca, represented in our seas 

 by the cuttle-fishes and nautili, creatures which, like 

 the crinoids, may be said to have had their birth in 



