GEOLOGICAL DISTRIBUTION OF ECHINODERMATA. 467 



united them in the living state having long since decayed away. 

 Their flat round form, and central perforation, have occasioned 

 them to receive the name of Entrochi, or wheel-stones. They 

 were formerly strung as beads for rosaries ; and in the northern 

 parts of Britain they still retain the appellation of St. Cuthbert's 

 beads. 



" On a rock by Lindisfarn 

 Saint Cuthbert sits, and toils to frame 

 The sea-born beads that bear his name." 



1025. The Pentacrinus first began to abound at the com- 

 mencement of the Lias ; and its remains present themselves in 

 great numbers in that formation, and in the Oolite which 

 succeeds it. From that period they diminish, and we gradually 

 lose sight of this interesting group, the few existing species 

 serving, as it were, but to indicate the structure of those, which 

 formerly occupied so important a rank among the inhabitants 

 of the ocean. As the Crinoidea disappeared, the other Stellerida 

 and Echinida took their place ; and remains of these are met 

 with in almost all marine strata, down to the present time. 

 being particularly abundant in the Chalk and Oolite. 



