MONOGRAPH OF THE EXISTING CRINOIDS. 167 



internal body septum; the first arm plates (radials) constitute the entire calyx. 

 Resting upon these first arm plates and the arm bases is the large visceral mass, 

 more than half of the total area of which is exposed. 



FIG. 104. LATERAL VIEW OF A SPECIMEN OF ANTEDON EIFIDA FROM PLYMOUTH, ENGLAND, SHOWING TUB RELATIVE PROPOR- 



TIONS OF THE ARMS, PINNULES, CENTRODORSAL, AND CIRRI, AND THE LNTERPRUIIBRACII1AL PLATES. 



In the majority of the holothurians the calcareous plates other than 

 spicules are wholly internal, and the entire body wall is soft. 



The crinoidal columnals have the same ultimate origin as the calyx plates; 

 but they arose, not directly from an aggregation of spicules ami plates, but sec- 



