90 ECHINODERMATA. CRINOIDEA. 



OBDEB. NEOCBINOIDEA. 



The calyx is small and the arms large, relatively. 

 Usually monocyclic, basals five. Inter-radials are seldom 

 present, there is no anal inter- radial. The radials of the 

 higher cycles are generally movable. There is no ventral 

 roof of plates. 



Apiocrinus. Calyx pear-shaped. Basals five, thick. 

 Three cycles of low radials, excavated on their upper 

 surfaces, all the plates firmly united. Arms ten, bifurcat- 

 ing once or twice, formed of a single row of plates. Stem 

 long, cylindrical, base expanded ; the articular surfaces of 

 the plates radiately striated. The plates of the upper 

 part of the stem are in contact at the periphery only, 

 leaving a space between each plate. The upper part of 

 the stem expands and passes gradually into the calyx, the 

 upper surface of the last plate is provided with five 

 radiating ridges between which the basals lie. Lias to 

 Lower Cretaceous. 



Marsupites. Calyx large, globular, plates large and 

 thin. Dicyclic. Stem absent. Base formed of a large 

 central pentagonal plate, the centro-dorsal plate. Under- 

 basals five, pentagonal. Basals five, hexagonal. Radials 

 five, pentagonal. Arms bifurcating, formed of a single 

 row of plates. Ventral surface of calyx covered with 

 small plates. Anus sub-central. Upper Chalk. 



Distribution of the Crinoidea. 



In comparison with its abundance in former times the 

 class Crinoidea is but poorly represented at the present 

 day. The most important family is the Comatulidse (e.g. 



