ECHINODERMA. CRINOIDEA 143 



coiled, anus near its base. Stem formed of low plates, often in five 

 pieces. Silurian and Devonian. Ex. B. decadactylus, Wenlock 

 Limestone. 



Poteriocrinus. Calyx with thin plates. Infra-basals equal. 

 Basals high. Three anal inter- radials present. Radials with well- 

 marked concave articular surfaces which do not occupy the entire 

 width of the plates. Anal tube long. Arms long, branching, with 

 pinnules. Devonian and Carboniferous. Ex. P. granulosus, Car- 

 boniferous. 



Woodocrinus. Allied to Poteriocrinus but calyx, arms, and 

 anal tube shorter. Carboniferous. Ex. W. macrodactylus. 



Encrinus. Calyx saucer-shaped. Infra-basals very small, 

 generally concealed by the stem. Basals rather large, hexagonal. 

 Radials large, pentagonal. Two fixed brachials in each ray, the upper 

 being axillary. No inter-brachials. Arms bifurcating, the branches 

 uniserial at first, then alternating, finally biserial ; with pinnules. 

 Tegmen covered with plates. Stem long, with small canal. Trias. 

 Ex. E. liliiformis, Muschelkalk. 



Pentacrinus. Calyx small, bowl-shaped, consisting of small 

 infra-basals, basals, and radials which projeot like spines over the 

 stem. Arms very long, much branched, uniserial ; the small 

 branches all come off on the same side of each main branch. The 

 arms bear pinnules. Stem long, pentagonal, with cirri coming off in 

 whorls ; the articular surfaces of the columnals with five raised, 

 crenulate, petaloid parts which are narrow and quite distinct from 

 one another. Jurassic. Ex. P. fossilis, Lias. 



Marsupites. Calyx large, globular ; plates large and thin. 

 Stem absent. Base formed of a large central pentagonal plate. 

 Infra-basals pentagonal. Basals hexagonal. Radials pentagonal, 

 with crescentic depressions for the articulation of the arms. Arms 

 relatively short, bifurcating, uniserial. Upper Chalk. Ex. M. testu- 

 dinarius. 



Ichthyocrinus. Three very small infra-basals ; five small 

 basals ; five radials ; two or three cycles of fixed brachials. Anal 

 inter-radial small, below the right posterior radial. Arms in 

 contact all round, uniserial ; no pinnules. Silurian to Carboniferous. 

 Ex. 1. piriformis, Silurian. 



