MONOGRAPH: OF THE EXISTING CRIXOIDS. 



349 



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

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

 centrodorsal the surface of this 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, corresponding 



Fio. 431. 



FIG. 432. 



Fias. 431-132. 431, THE CENTRODORSAL AND RADIALS OF A SPECIMEN OF PEROMETRA DIOMEDE.E FROM SOUTHERN JAPAN; THE 



ARTICULAR FACES OF THE RADIALS SHOW, WITHIN TIIF. MUSCULAR FOSSAE, SUPPLEMENTARY MUSCLE PLATES AND, JUST BELOW 



THESE, LIGAMENT BOSSES. 432, LATERAL VIEW (IF THE CENTRODORSAL AND RADIALS or A SPECIMEN OF 1'ONTIOMETRA ANDER- 



SONI FROM SINGAPORE SHOWING, ON THE ARTICULAR FACES OF THE RADIALS, THE SUPPLEMENTARY LIGAMENT FOSS.E 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 erhinoids. 



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

 five primitive divisions of the crinoid body; planes including the intcrbasul sutures 

 divide the crinoid into five morphologically equivalent sections. But the basals 

 alternate in position both with the infrabasals below and with the radials above 

 them. 



