312 



PALEOZOIC SYSTEM OF ROCKS. 



reaching half -way down the body (see Figs. 523-526, page 392). If 

 Crinids are comparable to inverted Star-fishes with many arms and set 



Fig. 327. 



Fig. 328. 



Fig. 320. 



Fig. 330. 



Fig. 331. 



Fig. 332. 



Figs. 327-332.— Silurian Crinoids: 327. Caryocrinus ornatus. 328. Pleurocystitis squamosus. 

 329. Pseudocrinus— a cystid restored (after Lutken). 330. Lepadocrinus Gebhardii. 331. Glyp- 

 tocrinus decadactylus (after Hall): a, specimen with arms; b, larger specimens without the 

 arms. 332. Ichthyocrinus sublasvis (after Hall). 



upon a stalk, the Cystids and Blastoids may be compared to Sea-urchins 

 similarly set. All these families are found in the Silurian. The Cys- 

 tids pass away with the Silurian, and are therefore characteristic of 

 that age. The Blastoids pass away before the end of the Carbonifer- 

 ous age, and are therefore characteristic of the Palaeozoic era, but espe- 

 cially of the Devonian and Carboniferous ages. The distribution of 

 the three orders in time is shown in diagram (Fig. 326). The Crinids 

 continue, though in diminished numbers, to the present day ; but of 

 course in very different families. Figures of Blastoids are given under 

 the Carboniferous, where they were far more abundant. 



