MONOGRAPH OF THE EXISTING CBINOIDS. 187 



plates form a solid capsule about the body which ia even more perfectly developed 

 than that about the body of the urchins. 



They possess a crinoid-hke column; the base is composed of three j)lates 

 beyond which are five large plates, each with a narrow (becoming broader with 



Fig. 120.— Lateral view of a specimen of PENTAMETBocBnros diouede^ from southwestern Japan, showino the 



RELATIVE proportions OF THE ARMS, PINNULES, CENTUOllORSAL, AND CIRRI. 



increasing specialization) cleft down the center occupied by a double row of small 

 plates; in the five interambulacral areas about the mouth arc five angular jjlatcs 

 of moderate size. 



The three large apical plates correspond to the five basals of the crinoids, and 

 to the five genitals of the urchins; infrabasals and oculars are not represented. 



