MONOGHAPH OF THE EXISTING CEINOIDS. 



349 



The five radials when united in their natural position form what is known as 

 the ratlial pentagon (figs. 11, 12, p. 65). Dorsally wliere it is joined to the 

 centrodorsal the surface of tliis radial pentagon as a whole is almost flat, though 

 the surface of each radial has a slight convexity resulting in usually shallow reentrant 

 furrows along the lines of suture between the individual radials (figs. 465-467, p. 359) . 



The crinoid radial is not a calyx plate at all, but a true arm plate, correspondmg 



Fig. 431. 



Fig. 432. 



Figs. 431-432. — (31, The centrodorsal and radial.s of a speomen op Terometra diomede^ from southern Japan; the 

 articular faces of the radlals show, "wtthin the muscular fossj., supplementary muscle plates and, just below 

 these, ligament bosses. 432, lateral view of the centrodorsal and radials of a specimen of tontiometra ander- 

 30NI FROM Singapore showing, on the articular faces of the radials, the supplementary ugauent foss^ on the 



OUTER portions OF THE TRANSVERSE RIDGE. 



exactly to each and every axillary; it is the equivalent of the asteroid teiminal, but, 

 as an entity, has no equivalent in the echinoids. 



The basals, lying directly over the five primary nerve trunks, indicate the 

 five prunitive divisions of the crinoid body: planes including the interbasal sutures 

 divide the crinoid into five mori)hologically equivalent sections. But the basals 

 alternate in position both ^\^tll the infrabasals below and with the radials above 

 them. 



