ECHINODERMA 



with its cirri remains attached to the animal, as the centr odor sal united 

 with the lowest cup plates, the infra ba sals. On the upper joint of the 

 stalk is a cup-shaped body (theca) the edges of which bear five or ten 

 (usually branched) arms. The walls of the theca are covered with poly- 

 gonal calcareous plates. 



FIG. 294. FIG. 295. 



FIG. 294. Pent acr inns ma'-hayamts (after Wyviile Thompson), br, brachialia; 

 c, cirri; d, distichalia; r, radialia; p, pinnuhf. 



FIG. 295. Different Pentacrinus stages (a, b, c) of Antedon rosacea. I, arms; 2, 

 cirri; 3, stalk. 



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

 alternating in order with the basalia (fig. 296). In some there is a circle of 

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

 the brachialia, are directly attached to the radials (fig. 296). But often the arm 

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

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

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

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



