228 THE VOYAGE OF H.M.S. CHALLENGER. 
rather more uniformly distributed over the apposed surfaces of the joints than those 
uniting the basals to the top of the stem. The upper surface of the basal ring presents 
five smooth and single sutural fossee for the attachment of the radials. They slope 
downwards and outwards from the edge of the central funnel, and each is marked near 
its outer edge by a single crescentic opening, or by two smaller ones in close proximity 
(PL VIla. figs. 12, 13). At first sight this more or less double opening would naturally 
be taken for the termination of the converging right and left forks of two adjacent 
interradial canals within the basal ring. This apparently obvious explanation is, however, 
very far from being the true one. The under faces of the radials which rest in these 
fossee on the upper surface of the basal ring are marked in the same way by more or less 
double openings ; but these are not the openings of the central canals, as the apparently 
similar openings are on the under faces of the radials of Pentacrinus and Metacrinus 
(Pl. XII. figs. 11, 22; Pl. XX. fig. 9; Pl. L. fig. 5). They are usually quite small and 
inconspicuous, and not nearly so well defined as the openings of the central canals on the 
distal faces (PI. VIla. fig. 15), with which indeed they have no communication, for they 
are merely small pits into which portions of the basiradial ligament are inserted ; and the 
same is the case with the corresponding openings in the 
fossee on the upper surface of the basal ring (PI. VIa. 
figs. 12, 13). Although the fibres of the basiradial 
ligament are generally distributed over the whole 
synosteal surface, they are more especially concentrated 
in ten bundles which are lodged in ten corresponding pits 
on each of the apposed surfaces of the basal and radial 
circlets. Owing to the curvature of these surfaces, 
these more defined bundles are not shown in the section 
represented in Pl. VIIb. fig. 3, which passes rather 
Besant cae cite cma ernie above their level through the general plane of the 
hianus, at the level of the upper part of the x ° 
basiradial oy ai, primary inter: synostosis ; but in the next section they are clearly 
peared Leaman maine visible, cut somewhat obliquely as shown in the woodcut 
(fig. 12,2). Bothin the woodcut, and in Pl. VID. fig. 3, 
the axial cords (az) are seen to be situated interradially. They retain this position 
until they reach about half the height of the radial pentagon, where they fork for the 
first time; and the branches enter the radials by the openings in their lateral faces 
(Pl. VII. fig. 6a). The right branch of one fork and the left branch of its neighbour 
in the adjoining basal occupy converging canals in the intervening radial, which meet 
almost directly, so that there is only one opening on the distal face (Pl. VIla. fig. 15). 
The circular commissure of Bathycrinus is thus mainly formed by the actual branches 
of the primary interradial cords, and not by special interradial commissures uniting these 
branches as in the Comatule and Pentacrinide (Pl. XXIV. fig. 9, cco). This is also the 
