TEEMINOLOaY. 37 



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 mmhy- 

 hsis, 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, i. e., 

 the arms uppermost, viewing the specimen from the anal side. The anal 

 interradius will then be posterior, the radius ojaposite 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 up, and the ventral view with the anal side down. Eight and 

 left remain the same in both cases. 



The ievxri^ proximal ^Vidi distal ^re 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 ujDper 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. Batlier the right and left "anterior" rays. The term is objectionable 

 because we have already the anterior ray proper. 



