148 FOSSIL CRINOIDS. 



Brachials cuneiform 



Ventral sac inflated 



balloon-shaped Coeliocrinus. 



mushroom-shaped Hydreionocrinus. 



Brachials quadrangular 

 Ventral sac short 



RA not touching IBB n. g. Z. elegans, etc. 



RA elongate, usually touch- 

 ing IBB Zeacrinus. 



Rays usually not branching beyond IIBr or IIIBr 

 Arms dichotomous 



Ventral sac long, rising to height of 

 arms 

 Arms 10 

 Calyx depressed 



Sac not forking Decadocrinus. 



Sac forking Aulocrinus. 



Calyx elongate Scytalocrinus. 



Ventral sac inconspicuous or wanting 

 Base not concave; IBB large, 

 visible 

 Arms 5 or 10 



Brachials quadrangular 

 to cuneiform, tending 



to biserial Crojiiyocrinus. 



Anal X above RR Ulocrinus. 



IBB undivided; stem- 

 less Agassizocrinus. 



Base concave; IBB at bottom of 

 funnel 

 Arms 10 to 20 



Brachials quadrangular 



to biserial Eupachycrinus. 



No Radianal 



Radial facets straight, filling face of R. 



Anal X between RR. resting on post. B. 

 Rays branching more than once 



Arms dichotomous, abutting Bursacrinus 



