144 



ECHINODERMA. CRINOIDEA 



Sagenocrinus. Infra-basals small. Anal inter- radial sunk 

 between basals ; radials large. Numerous cycles of fixed brachials, 

 separated by very numerous inter-brachials. Arms dividing, uni- 

 serial ; no pinnules. Silurian. Ex. S. expansus. 



Apiocrinus (fig. 58). Calyx large. Infra-basals enclosed by, 

 and often fused with, the thick 

 basals. Radials low, excavated 

 on their upper surfaces. Four 

 cycles of fixed brachials. Arms 

 ten, bifurcating once or twice, 

 uniserial. Stem long, cylindrical, 

 base expanded ; the articular 

 surfaces of the columnals radi- 

 ately striated. The upper colum- 

 nals are in contact at the periphery 

 only. The upper part of the stem 

 expands and passes gradually into 

 the calyx ; the upper surface of 

 the last columnal is provided with 

 five radiating ridges between 

 which the basals lie. Lias to 

 Lower Cretaceous. Ex. A. 

 kinsoni, Bradford Clay. 



par- 



Fig. 58. Apiocrinus parkinsoni, 

 from the Bradford Clay, s, top 

 columnal of the stem ; /;, basal 

 plates ; r, radial plates ; 2, 3, 

 and br, fixed brachial plates. 



Millericrinus. Allied to Apiocrinus. Usually the top 

 columnal only is widened. Articular facets of radials and brachials 

 well developed. Lias (1 also Trias) to Lower Cretaceous. Ex. 

 M. pratti, Inferior and Great Oolite. 



Bourgueticrinus. Calyx small, with vertical or inwardly- 

 sloping sides ; basals about half the height of radials ; two 

 rows of fixed brachials ; no inter-brachials. Free arms unknown. 

 Stem long, the top columnal very large, as wide as calyx ; upper 

 columnals with circular, others with elliptical articular faces 

 and a transverse ridge across the longer diameter. Cretaceous. 

 Ex. B. ellipticus, Chalk. 



