NO. IO PHYLOGENETIC STUDY OF RECENT CRINOIDS CLARK 5 1 



Disk 

 2. Disk naked. 

 2. Orals absent, 

 i. Mouth central. 



Arms 



2. Arms dividing one or more times, but without IBr series. 



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



the second post-radial ossicle, 

 i. A suture between the ossicles of the IBr series, 

 i. Division series composed of an irregular number of ossicles. 

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

 i. All the arms of equal length, 

 i. All the arms terminating in a growing tip. 

 i. All the arms provided with ambulacral grooves. 



Pinnules 



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



i. All of the pinnules similar. 



i. Pinnulation of the arm bases more or less deficient. 



2. Side- and covering-plates rudimentary. 



i. All of the pinnules provided with ambulacral grooves. 



General 

 2. Skeleton composed of less than a million ossicles. 



BOURGUETICRINID^E 



Calyx 



2. Calyx forming a platform upon which the viscera rest, more or 



less supported by the arm bases, 

 i. Calyx reduced by the moving inward of all the calyx plates, 

 i. Basals present, 

 i. Five basals. 



i. Basals separate (half). 



2. Basals fused into a single calcareous element (half). 

 2. No infrabasals. 



1. Five radials. 



2. Interradials absent. 

 2. Anal x absent. 



2. Interbrachials absent. 



