ECHINODERMATA, 



155 



PLATE XXI 



PENTACRINOID LARVA OF ANTEDON (Original). 



Fig. 1. Skeleton of early Pentacrinoid, under Black-ground illumination, showing its component 

 plates: 6, 6, basals, articulated below to the highest point of the stem; r 1 , r 1 , first radials, between 

 two of which is seen the single anal plate, a; r-, second radials; r 3 , third radials, giving off the 

 bifurcating arms at their summit; o, o, orals. 



2, 3. Back and front views of a more advanced Pentacrinoid, as seen by incident light, one of 

 the pair of arms being cut away in Fig. 3, in order to bring the mouth and its surrounding parts 

 into view : 6,6, basals ; r 1 , r 8 , r 3 , first, second, and third radials; a, anal, now carried upwards by 

 the projection of the vent v: o, o, orals; cir, dorsal cirrhi, developed from the highest joint of the 

 stem. 



