300 



ECHIXODER^IA 



with its cirri remains attached to the animal, as the coilrodorsa! united 

 with tlie lowest cup plates, the iii/rabjsals. On the upper joint of the 

 stalk is a cup-shaped body (li'iccj) the edges of wliich bear t'lve or ten 

 (usually branched) arms. The walls of tire theca are co\"ered with poly- 

 gonal calcareous plates. 



Fig. 294. Fig. 295. 



Fig. 294. — PeiilLia-i}ius in,!il:ayainis (aflcr Wvyillc Thompson"), br, brachialia; 

 c, cirri; </, distichalia; r, radialia; />, pinnulLO. 



Fig. 295. — Different Fcntdcrinus stages ^a, l\ c) of AntcJon rosacea, i, arms; 2, 

 cirri; 3, stalk. 



Usually the stalk bears five plates, the hasalia, and then come five radialia, 

 alternating in order with the basalia i^lig. 290). In some there is a circle of 

 infrabasalia in a line with the radiaha. Frequently the elements of the arm, 

 the hracliialia, are directly attached to the radials (fig, 206). But often the arm 

 branches once or several times dichotomously, and the first branching takes 

 place at the base, so tliat the arms seem to spring from the theca. In these 

 cases the first lirachialia are considered as part of the theca and are called 

 radialia disliclialia (fig. 294). From the arms arise, right and left, a row of 



