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 being 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 fossze 
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 still 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 
fossee 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 rawsont, owing to the greater size of the lateral fossze. Hach is 
denticulate along its median line, as in the other Bourgueticrinide. 
The distinction of the lower stem-joints of Rhizocrinus and Bathycrinus thus becomes 
a matter of some difficulty, 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. VIIIa. figs. 2,3; Pl LIIL. figs. 7, 8; 
woodcut, fig. 16, p. 244). 
The lower part of the stem in the Bourgueticrinide 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) ; while 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- 
