REPORT ON THE CRINOIDEA. 27 



assumes an oval form, and the ten markings on its edge first become arranged into two 

 groups of five each (fig. 5), and then finally disappear (fig. 6). This is due to the five 

 ligamentous bundles mentioned above as beiag attached to the basals, becoming 

 gradually replaced by the two larger and somewhat crescentic bundles which unite 

 the joints lower down the stem. The articular rim eventually becomes restricted 

 to a broad ridge which occupies the short axis of the oval oblong face, and is pierced 

 in the centre by the oval opening of the central canal (figs. 7, 8). In the slender joints 

 of the upper third of the stem (fig. 7) this ridge takes up the greater part of the 

 articular surface, and there is merely a shallow fossa on either side of it. As the 

 joints increase in stoutness the ridge becomes relatively narrower, and the lateral fossae 

 proportionately larger (figs. 8, 9). They are shallowest at the edge, and gradually 

 deepen as they approach the ridge. When the joints begin to shorten again but 

 continue to increase in stoutness, their terminal faces become more circular (fig. 10), 

 though the planes of the articular ridges at the two ends of each joint stUl continue 

 to cross one another. The ridges themselves still diminish in relative width, and 

 become somewhat constricted in the middle, until there is only a very narrow rim 

 around the opening of the central canal (figs. 9, 10). Lower down the stem this rim 

 disappears altogether (PI. VII. figs. 12, 13; PL Vila. fig. 11), so that the two lateral 

 fossse communicate around the central opening just as in Rhizocrinus (PL X. 

 figs. 11-14). 



The joint-faces also become oval again, and the articular ridges now occupy their 

 longer axis (PL Vila. fig. 11) instead of the shorter ones, as is the case at the top 

 of the stem (figs. 7-9). The two halves of each ridge which are separated by the 

 opening of the central canal are of an elongated triangular shape, and relatively narrower 

 than in Rhizocrinus raivsoni, owing to the greater size of the lateral fossse. Each is 

 denticulate along its median line, as in the other Bourgueticrinidse. 



The distinction of the lower stem-joints of Rhizocrinus and Bathycrinus thus becomes 

 a matter of some difiiculty, though those of the upper and middle parts of the stem are 

 very different in their characters. 



In the young individuals of both genera most of the stem-joints are simple, more 

 or less elongated cylinders ; and the characteristic dice-box shape is only visible in 

 a few joints immediately above the root (PL Villa, figs. 2, 3 ; PL LIII. figs. 7, 8 ; 

 woodcut, fig. 16, p. 244). 



The lower part of the stem in the Bourgueticrinidse may bear a large number of 

 irregularly branched radicular cirri, two or more proceeding from each joint near the end 

 of the long axis of one face (PL IX. fig. 1 ; PL X. figs. 13, 15) ; whde the main axis may 

 eventually break up into a similar set of branching rootlets. These two forms of roots 

 may coexist in the same individual, or either may occur alone. In some specimens of 

 Rhizocrinus lofotensis the radicular cirri are exceedingly abundant. Thus in an indivi- 



