48 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 



Arms 



1. Arms composed of a linear series of ossicles, without IBr 



series (minority). 



2. Arms dividing one or more times, or, if undivided, with IBr 



series (majority). 



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



(majority). 



2. Arms with IBr series in which the outer element is not axil- 



lary (minority). 



1. The first bifurcation is at a more or less indefinite distance 



beyond the second post-radial ossicle (minority). 



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



(majority). 



1. A suture between the ossicles of the IBr series (minority). 



2. A ligamentous articulation in the IBr series (majority). 



1. Division series composed of an irregular number of elements 



(minority) . 



2. Division series composed of a fixed number of elements 



(majority). 



1. The arms occupy only a portion of the border of the radials 



(minority) . 



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



(majority). 



1. All the arms of equal length (majority). 



2. The posterior arms dwarfed (minority). 



1. All the arms terminate in a growing tip (majority). 



2. Some of the arms end in a pair of pinnules (minority). 



1. All of the arms are provided with ambulacral grooves 



(majority). 



2. The posterior arms are without ambulacral grooves (minor- 



ity). 



Pinnules 



1. Pinnules, at least the proximal, more or less sharply triangular 



in cross section (majority). 



2. Pinnules circular or elliptical in cross section (minority). 



1. All of the pinnules similar (minority). 



2. The proximal pinnules modified (majority). 



1. Pinnulation of the arm bases more or less deficient (minor- 



ity). 



2. All of the proximal pinnules present (majority). 



1. Side- and covering-plates highly developed (minority). 





