390 The Calceocrinidm. 



This peculiar conformation, the hinge on one side of the piece, and 

 the mobility of the opposite side, allowed the basal piece to swing upon 

 its hinge like a door or lid, — or, more strictly speaking, allowed the ra- 

 dial portion of the calyx to erect itself upon the basal portion. This 

 function was possessed in variable degrees by the different species. 



The incurved portion normally lies within the surface of the crinoid 

 when it is at rest, allowing the column, which is inserted into the con- 

 vexity formed by the curvature, to rest against the arch receiving this 

 portion; and in those species in which the column is straight, or nearly 

 so, and which have the calyx resting against it, the calyx is at times 

 somewhat grooved beyond this point for its reception. Margin of the 

 calyx very irregular, rising into high acute points laterally, with a de- 

 pression between them on the anterior side and a deeper one on the 

 posterior side. 



Calyx composed of two rings of plates, whose number and position 

 vary somewhat in the different genera, due to anchylosis and the modi- 

 fication of some of their functions, but they have the same general dis- 

 position in all. 



The first or basal ring forms the consolidated basal piece; this is com- 

 posed of three or four plates, consisting of two anterior basals or their 

 anchylosed equivalent, and two lateral basals. The two lateral basals 

 are the largest, and, taken together, they form the entire posterior mar- 

 gin of the piece extending to the outer angles. The point of attach- 

 ment for the column is always upon the line of their union, while the 

 apices of the anterior basals may or may not enter into the formation 

 of the columnar facet. These plates together form a somewhat lunate- 

 shaped piece, and are usually not anchylosed. ^ 



The anterior basals or their anchylosed equivalent are triangular, and 

 occupy the median portion, or the whole, of the anterior margin. 

 When the two anterior basals are not anchylosed, the dividing suture- 

 line is a continuation of the one separating the lateral basals, and 

 divides the piece into equilateral halves. As they are of equal size and 

 shape, they will — for the sake of brevity — be described only in the an- 

 chylosed form. 



Anterior anchylosed basal triangular, with the inner angle at times 

 prolonged into a slender process extending up to or towards the 

 column. Suture-lines between it and the lateral basals generally 

 sinuous. 



The second or radial ring contains from six to eight plates, of 

 which the anterior radial and the lateral radials can always be 

 made out, while the posterior radials are generally separate, though 



^ In all species which I have had an opportunity to examine, the 

 dividing suture-line could be made out, including several figured by 

 their describers as being anchylosed. 



