NO. IO PHYLOGENETIC STUDY OF RECENT CRINOIDS CLARK 53 



1. Five radials. 



2. Interradials absent. 

 2. Anal x absent. 



2. Interbrachials absent. 



Column 



1. Entire column present. 



2. Column un jointed. 



2. Column not composed of short cylindrical ossicles with radial 

 crenellas. 



1. Column terminating in an expanded terminal stem plate. 



2. Radicular cirri absent. 

 1. Cirri absent. 



Disk 



1. Disk entirely covered with plates. 



1. Orals present. 



2. All five orals of the same size. 

 2. Orals a spherical triangle. 



1. Mouth central. 



Arms 



2. Arms dividing once, with IBr series. 



1. Arms with IBr series in which the outer element is axillary. 



2. The first bifurcation is on the second post-radial ossicle. 



2. A ligamentous articulation between the elements of the IBr series. 



2. Division series composed of a fixed number of ossicles. 



2. The arms occupy the entire distal border of the radials. 



2. The posterior arms are dwarfed. 



1. All the arms terminate in a growing tip. 



1. All the arms are provided with ambulacral grooves. 



Pinnules 



1. Pinnules more or less sharply triangular in cross section. 



1. All of the pinnules similar. 



2. All of the proximal pinnules present. 



1. Side- and covering-plates highly developed. 



1. All of the pinnules provided with ambulacral grooves. 



General 



2. Skeleton composed of less than a million ossicles. 



