HEXACRINID^ W. and Sp. 



Monocyclic. Radials in contact except at the posterioe side, where thet are 



SEPARATED BY AN ANAL PLATE. BaSALS FORMING A HESAGON. STRUCTURE OTHER- 

 WISE AS IN THE PLATYCRINID^. 



Analysis of the Genera, 



A. Basals 3. 



1. Costals 1 or 2. 



Arms in form of main trunks giving off lateral branches ; uni- 



serial 



Arms branching, biserial. Plates of the calyx, and some 

 of the free brachials, covered with movable spines 



B. Basals 2. 



1. Costals 2, forming a sxjzygy. 



Plates thin, column round 



Column crescent-shaped, giving off two rows of long cirri . . 



2. Costals 1 ; trigonal, very small, sometimes hidden hy the disfichals, 



with first palmars touching the radials ; arms biserial. 

 Plates thick ; anal plate in form and size resembling the 



anterior radial 



Anal plate much smaller than the radials; radial dome plates 



produced into wing-like appendages 



Hexacrimis. 

 Arthracantha. 



Dichocrinus. 

 Camptocrinus. 



Talarocrinus. 

 Pterotocrinus. 



