HEXACRINIDZ. 43 
Fig. 22. 
Fig. 20. Fig. 21. 
6=basals; R=radials; «= special anal plate; s = syzygy. 
ftemarks. —'The Hexacrinide are closely allied in general structure and 
habitus to the Platycrinide, but are at once distinguished, as already pointed 
out in the remarks upon that family, by having a large anal plate between 
the two posterior radials, and a hexagonal base, the basals thus supporting 
six plates, instead of five. The base of the Hexacrinidse may be composed 
either of three plates, or only two; but-in either case the plates are sub- 
stantially equal, and form a cup with six salient angles, and either two 
or three re-entering angles at the upper margin. When the base is bipar- 
tite, the suture runs from the anal plate to the anterior radial; but when it 
is tripartite, the sutures are directed to the anal plate and the right and left 
antero-lateral radials. In either case, therefore, there is always an interbasal 
suture running to the middle of the anal side, whereas in the Platycrinide 
the nearest interbasal suture to the anal side runs to the middle of the right 
posterior radial. 
The genera which we refer to the Hexacrinide were always placed 
among the Platycrinids until we separated the two families,* and further 
investigation only confirms the validity of their separation. It is based on 
a fundamental structural modification, for which we find an exact parallel 
* Revision, Part IIT., p. 93. 
