io8 



THE CRINOIDEA 



proximal columnal is always the youngest. In another type the 

 proximal columnal is one of the first formed, and remains attached 

 to the cup, new nodals being introduced below it (Fig. XVII. 

 4-7). This proximal columnal is called article basal by P. de 

 Loriol, and " centro-dorsal " by others, erroneously. It is here 

 called the proximate. 



The Connection between the Elements of the Crinoid Skeleton 

 is primarily by means of the fibrils of the stroma in which they 

 are deposited. This condition persists in the " primitive suture," 

 and from it development proceeds in the direction of either 

 greater rigidity or greater flexibility. Towards rigidity we have : 

 (1) "Close suture," in which the fibres are short, and their ends 

 surrounded by denser layers of stereom on the apposed surfaces of 



4 



.B 



Fio. XVII. 



The Relations of the Stem. 1, portion of stem of Gastrocrinus patulus (modified from Jaekel), 

 the latest formed columnals are numbered 1, the oldest 6 ; 5 and 6 bear cirri. 2, proximal, and 



mg mirauasais (IB) fused to proximale (P). 5, proximale of Apiocrinus elegans, Defr., showing 

 depressions for BB (Brit. Mus. E6711). 6, cup and part of stem of A. elegans, showing 

 proximale and other enlarged columnals (based on Brit. Mus. E6709 and E6710). 7, portion of 

 cup and stem of Millericrinus polydactylus (modified from P. de Loriol), showing minute 

 infrabasals attached to proximale, also new columnals forming (1). 



the ossicles, which are thus closely and immovably fitted together, 

 though separable by alkalies. (2) " Syzygy," a special case of close 

 suture between brachials or columnals (Fig. XVIII. 2, 3, and 4), 

 in which the upper ossicle, " epizygal," bears a pinnule or cirri, 

 as the case may be, and the lower one, " hypozygal," bears none. 

 (3) " Anchylosis " or fusion, when two ossicles are immovably 

 cemented by an unbroken deposit of stereom, which, however, 

 is less solid than that of the plates themselves. Towards flexibility 

 we have : (1) That form of "loose suture" in which the stroma- 

 fibrils lie at right angles to the suture, and the stereom is thrown 

 into corresponding folds (cf. pore -rhombs of cystids), or that form 

 in which there is a slight facet, either smooth or striated (Fig. 

 CXI. 3), or interlocking crenulations (Fig. XVIII. 1). (2) " Imper- 

 forate articulation," in which there is a slight facet, or a toothed 



