ECHINODSBMATA MORPHOLOGY OF SKELETON 329 



(often even very small) part of it; other plates take part in its 

 structure, as we shall see more in detail when describing the peri- 

 somatic skeleton. The border of radials round the apical capsule 

 becomes more or less markedly disturbed by the appearance of 



- \OA1S 



FIG. -2SO. Apical system of Cyatho- 

 crinus. For lettering see p. 317. <""/<. Anal 

 interred iaL 



FIG. 29u. Marsupites ornatus. P! 

 the dorsal cup. For lettering see p. 317. 



i .-A 



special ' anal plates " in the posterior unpaired interradius ; these 

 specialised anals occur very frequently in palaeozoic Crinoids (Fig. 291). 



The Crinoids with dieyelie base (with infrabasals, Figs. 289 

 and 290) are : (a) most Iimdumtta ; (b) among the Canierata, the 

 families of the ReteocrinidiR p. p., 

 Glyptasterid^, and 

 (c) the Articulatn. 

 (Ichthyocrinida) ; (d) the Camilieu- 

 lafa, in which, it is true, the infra- 

 basals are often either fused with 

 the uppermost joint of the stem 

 or atrophied, at least in the adult : 

 such are conveniently termed 

 Pseudomonoeyelie. 



The Crinoids with monoeyelie 



base (without infrabasals, Fig. 291) 



are, apart from a few Inadnnata, 



the Camerate families of the 



I'.iinocrinidce, Phity- 



B:irra ndeocrin <d<r, Eu<vluijh><-r' ( n idee.} 



Instead of the typical five infrabasals and five basals there are 

 very often found four, three, or even only two plates in these rings ; 

 this is especially the case in extinct Crinoids belonging to the orders 

 I/<"du/>fii. . and Arfwhtf-.i. The plates are then almost 



FIG. 291. Actinocriuus proboscidalis. Plates 

 f the dorsal J/\^ lettering see p. 317. 



