THE ECHINODERMATA 



247 



of feeding (microphagous) is fundamentally the same as in 

 brachiopods and lamellibranchs, but the structures 

 adapted to the same ends are fundamentally different. 



Not to be confused with the food-grooves are longi- 

 tudinal cavities, elliptical in section, in the substance of 

 the brachial and radial plates : these are the axial canals 

 and contained a nerve-cord. 



iBr. 



Br. 



Ax, 



-A.F. 



a. 



Br. 



FIG. 68. AMPHORACRINUS ATLAS (M'Cov), VISEAN (CARBON- 

 IFEROUS LIMESTONE), YORKSHIRE. 



a, Side view ; b, base. (Natural size.) (Original.) A, Anal plate inter- 

 calated between radials ; A.F., facet to which arm is articulated; 

 Ax. t axillary plate (primaxil) ; Br. , brachial plate (primibrach) ; 

 i Br., interbrachial plate (inter-primibrach) ; R, radial plate. 



2. Amphoracrinus atlas (Fig. 68) is a not uncommon 

 fossil in the Carboniferous Limestone knolls of Clitheroe 

 and elsewhere in the North of England. Usually the 

 calyx is found without arms or stem. The columnals are 

 abundant, though not with certainty distinguishable from 

 those of allied forms. Their articular surfaces show fine 

 radiating lines and a pentagonal axial canal. 



There are no infrabasals (monocyclic) and the basals 

 are reduced to three by crowding, leading to fusion. The 



