ECHINODERMA. CRINOIDEA 141 



Tegmen with small plates ; anus sub-central, sometimes at the end 

 of a long process. Stem long, section often elliptical. Devonian, 

 but mainly Carboniferous. Ex. P. Icevis, Carboniferous Limestone. 



Eucalyptocrinus ( = Hypantkocrinus). Calyx deeply con- 

 cave at the base ; at the bottom of the cavity four basals, at the 

 sides five radials ; several cycles of fixed brachials, and some inter- 

 brachials. Tegmen elevated, and forming a central anal tube com- 

 posed of five rows of large plates. Ten vertical partitions spring 

 from the outside of the tegmen, forming compartments in which the 

 ten arms rest. Arms biserial except at the base. Silurian and 

 Devonian. Ex. E. decorus, Wenlock Limestone. 



Actinocrinus (fig. 56). Calyx pear-shaped, ovoid, or more or 

 less spherical. Basals three, equal, forming a hexagon. Radials 



OP* 



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Fig. 56. Diagram of the plates of Actinocrinus triacontadactylus, Carboni- 

 ferous Limestone, b, basal plates ; r, radials ; 2, 3, fixed brachials ; 

 br, brachial plates ; ir, inter-brachials ; a, anal inter-radial. 



generally higher than wide. The first two rows of brachials firmly 

 united. Inter-brachials numerous ; and also one (posterior) inter- 

 radial, above which the inter-brachials are more numerous than in 

 the other areas. Tegmen formed of thick, tubercled, hexagonal 

 plates, produced into a tube with the anus at the end. Arm- 

 branches ten to thirty, biserial. Stem circular, canal pentagonal. 

 Carboniferous. Ex. A. triacontadactylus, Carboniferous Limestone. 



