§ 39. ENCRINITES AND PENTACRINITES. 649 



and of the peduncle or process of attachment, by which the 

 base of the column was permanently fixed to the rock. The 

 separate bones of the column were called trochites, or wheel- 

 stones, by the early collectors ; and several united, entro- 

 chites. In the north of England they were popularly 

 known by the name of fairy -stones, and St. Cuthbert's 

 beads : the circular perforated kinds are occasionally found 

 in tumuli, having been worn as ornaments by the ancient 

 Britons. These bodies present considerable variety in 

 form, and their articulating surfaces are marked with 

 diversified floriform and stellular figures ; as in the series 

 of specimens before us (Lign. 145). The central perfora- 

 tion, which is circular and very small in some species, 

 and large and pentagonal in others, forms in the united 

 column a channel from the receptacle to the base, which 

 is supposed to have contained a chord of nervine or me- 

 dullary matter. The inner part of the ossicula seems to 

 have been more perishable than the external zone ; for the 

 latter is often filled up either with spar, or the material 

 of the surrounding rocks. In the siliceous veins and 

 bands of chert that pervade some of the limestones of 

 Derbyshire, the curious fossils termed pulley- stones often 

 occur ; these are casts formed by the infiltration of 

 silex into the cavities of encrinital columns {L'tgn. 145, 



fig. i). 



The skeletons of the Crinoidea, like the stony fabric of 

 the corals, were, of course, secreted by the animal mem- 

 brane ; and, as in the fossil tubipore (ante, p. 645), this 

 tissue may be detected. Upon submitting some encrinital 

 ossicula from the Derbyshire limestones to the action of 

 weak acid, the calcareous earth was removed, and the origi- 

 nal membrane appeared in transparent flocculi.* 



40. Derbyshire encrinital marble. — Some of the 



* See Parkinson's Organic Remains, vol. ii. p. ]6Q. 



