HEXACRINIDA W. and Sp. 
Monocycuic. RADIALS IN CONTACT EXCEPT AT THE POSTERIOR SIDE, WHERE THEY ARE 
SEPARATED BY AN ANAL PLATE. BASALS FORMING A HEXAGON. STRUCTURE OTHER- 
WISE AS IN THE PLATYCRINIDA. 
Analysis of the Genera. 
A. BASALS 3. 
1. Costals 1 or 2. 
Arms in form of main trunks giving off lateral branches; uni- 
SORIA] ve ca: <aigette tenes abate eae en en ee Hexacrinus. 
Arms branching, biserial. Plates of the calyx, and some 
- of the free brachials, covered with movable spines . Arthracantha. 
B. Basaus 2. 
1. Costals 2, forming a syzygy. 
Plates thin, column round. 
‘Column crescent-shaped, giving off two rows of long cirri. . Camptocrinus. 
2. Costals 1; trigonal, very small, sometimes hidden by the distichals, 
with first palmars touching the radials ; arms biserial. 
Dichocrinus. 
Plates thick; anal plate in form and size resembling the 
Anterior Ladia ls. Saco ee ae ne ee ee ee Talarocrinus. 
Anal plate much smaller than the radials; radial dome plates 
produced into wing-like appendages .. . Pterotocrinus. 
