TERMINOLOGY. 3 
The plates of a Crinoid are united either by suture or by muscular 
articulation. The former may be a close suture, a loose suture, or an anchy- 
sis. A close suture is nearly or perfectly rigid; the apposed faces are flat, 
and may be smooth or striated. In a loose suture the faces are more or less 
concave or excavated, lodging bundles of ligament, so as to give to the 
plates a considerable amount of mobility. An anchylosis is a modified close 
suture, in which the lines of union have been obliterated by subsequent 
limestone deposit. In a muscular articulation, the apposed faces are per- 
forated, and provided with a transverse ridge, or a sort of ball-and-socket 
joint. 
The orientation is based upon the natural position of the Crinoid, 7. e., 
the arms uppermost, viewing the specimen from the anal side. The anal 
interradius will then be posterior, the radius opposite to it anterior, and 
right and left will correspond with the right and left of the observer. Next 
to the anterior ray are the two antero-lateral rays,* and adjoining the anal 
interradius the right and left posterior rays. Corresponding appellations are 
applied to the interradial spaces, which consist of the two anterior, the two 
antero-lateral, and the posterior or anal, interradii. 
In illustrating the plates of the calyx, the dorsal view is figured with the 
anal interradius wp, and the ventral view with the anal side down. Right and 
left remain the same in both cases. 
The terms proximal and distal ave reckoned from the chambered organ, so 
that the infrabasals and the top-stem-joint are the proximal elements of 
crown and stem respectively. In the crown, the outer surface of a plate 
represents the dorsal side, its lower edge the proximal face, its upper edge 
the distal face, and the faces at the sides are the lateral faces. In the stem, 
however, the upper face is the proximal, and the lower one the distal. 
* These rays are called by Mr. Bather the right and left “anterior” rays. The term is objectionable 
because we have already the anterior ray proper. 
