20 SMITHSONIAN INSTITUTION 



plates between the rays which lie within the radial circlet, like the first plate in 

 the Rhodocrinidae; this must therefore be included within the general term 

 " interradials," while new and ponderous terms (intersecundibrachs, etc.) must 

 be provided for plates between the ray divisions. This is confusing and wholly 

 unnecessary, the former use of the terms being self-explanatory. While ad- 

 hering to the term " interbrachial " with the symbol iBr, as now generally 

 employed, I shall reserve the liberty to use the term " interradials " freely in 

 discussion to describe all plates dorsally situated between the rays, whether in 

 the zone of the radials or above. For those in the tegmen the term " inter- 

 ambulacrals " is sufficient. 



For encyclopedic collections and definitions of terms employed in connec- 

 tion with the Crinoidea, I refer to Bather's chapters in the Lankester Zoology, 

 and to Clark's Monograph of the Existing Crinoids, 1 the first volume of which 

 appeared in 1915. For the purposes of the present work the following list, 

 largely adopted from the Camerata monograph, is deemed adequate : 



Explanation of Terms 



Column or stem. The jointed appendage attached to the dorsal end of the calyx. It is 

 composed of segments or ossicles called columnals, which are either nodals (cirrus-bearing) 

 or internodals (interpolated segments). The longitudinal canal running through the center 

 of the stem into the calyx is the axial canal. When speaking of the form of the stem the trans- 

 verse section is meant. The top columnal is called the proximate. 



Arms. Jointed appendages toward the ventral pole of the calyx, formed by the outward 

 extension in a radial direction of apposed projections of the dorsal wall and ventral perisome 

 given off at the line of union between these two structures. They may be either simple or 

 branching; composed of one series of brachials (uniserial) , or of two interlocking series 

 (biserial) ; if they branch by substantially equal bifurcations they are called dichotomous, if 

 unequally by lateral ramules, which may branch again, usually separated by one or more 

 brachials, — heterotomous. Both arms and ramules may be fringed with still smaller appen- 

 dages called pinnules given off at alternate sides from every successive brachial, or sometimes 

 from both sides of each ; the component ossicles of the pinnules are called pinnulars. Neither 

 simple nor biserial arms, nor pinnules, are known in the Flexibilia. 



Crown. The crinoid minus the column. 



Calyx. The crinoid minus the column and free arms. 



Dorsal cup. All parts of the calyx below the origin of the free arms. 



Tegmen. That part of the calyx lying above the origin of the free arms, being the 

 integument covering the viscera ; it embraces the disk-ambulacra, the mouth, and usually the 

 anus ; and it is synonymous with the terms disk, ventral disk, vault, dome, summit. 



Base. That part of the dorsal cup lying next to the column. It may be composed of one 

 ring of plates {monocyclic') , or of two rings (dicyclic), which are distinguished as infrabasals 

 (IBB), and basals (BB). The infrabasals, when present, form the proximal ring, and are 

 radially disposed. The basals adjoin the radials and alternate with them, being interradial in 

 position. By the law of Wachsmuth and Springer, 2 the elements of the crinoid skeleton from 

 radials down to cirri successively alternate with each other in position ; so that in descending 

 order from the radially situated infrabasals in a dicyclic crinoid the pentameres of the stem 



1 Clark, A. H., Bull. 82, U. S. National Museum, pp. 59-108. 



1 North American Crinoidea Camerata, 1897, p. 60; Bather in Lankester, Zoology, pt. 3, 1900, p. 106. 



