THE CRINOIDEA 



123 



Inadunata and Flexibilia ; in the former group the small plate 

 is often, but not always, the anterior infrabasal (Fig. XXXI. 7) ; 

 in the latter it is (apnd W. and Sp.) always the right posterior 

 infrabasal (Fig. XXXI. 8). A bipartite base is formed only in a 

 few Monocyclica ; the two plates lie on the right and left sides of 

 the cup (Fig. XXXI. 9). Finally, all plates of the proximal circlet 

 may fuse into a solid ring, both in Mono- and Di-cyclica. The 

 infrabasals may fuse with the proximal columnal in Flexibilia, 

 thus forming a pseudomonocyclic type. The basals may be over- 

 grown by, and incorporated with, the radials, as in Eufjcniacrinus. 

 The symmetry of the base is modified by the presence of anals. 

 An anal resting on the basal circlet causes one of the basals to 

 double in width, so that the base becomes hexagonal instead of 

 pentagonal. Thus the quadripartite base comes to consist of a 



FIG. XXXI. 



Bases and their modifications. 1-0 

 and 9, inonocyclic ; 7 and 8, dicyclic ; 

 1-4, pentagonal, unaffected by anal ; 

 5, 6, 9, hexagonal, affected by anal. 

 In all the anal side is uppermost, and 

 the plates are numbered on Jaekel's 

 plan (see table, p. 110) ; the imagin- 

 ary additional piece is inarked + . 

 1, 5 BB ; 2,4 Un ; 3, 3 JiJf, Crinoid 

 type ; 4, 3 JiJS, Blastoid type ; 5, 

 4 J:B ; 6, 3 Bit ; 7, 3 IttB, as usual in 

 Dicyclica inadunata; 8, 3 I Jill, as 

 usual in Flexibilia imjrinnata ; 9, 

 2 JiJi. (Adapted from Wachsmuth & 

 Springer.) 



posterior and anterior large plate, and two small lateral plates (Fig. 

 XXXI. 5). These tend to approximate in size. In Xenocrinus 

 (Fig. LXXVIIL), interbrachials as well as anals come down between 

 the radials, so that the basals are nearly equal in size, but irregular 

 in shape, and make the base decagonal. Removal of anals and 

 interbrachials from the radial circlet leaves a pentagonal quadri- 

 partite base, such as is found in Melocrinidae (p. 161). An anal 

 resting on a tripartite base is accompanied by increased width in 

 the small left anterior basal (Fig. XXXI. 6). But in the bipartite 

 base the small basal fuses with the combined posterior and left 

 posterior basals, while the combined right-hand basals increase in 

 width (Fig. XXXI. 9). In most Dicyclica the infrabasals do not 

 assume a hexagonal outline ; for the anals do not occur in the 

 basal circlet, but x truncates the upper surface of the posterior 

 basal. Exceptions are Sagenocrinus, Cardbocrinus (Fig. LXXXIV.), 

 Strophocrinus, and Thenarocrinus (Fig. XCVL). 



