230 THE VOYAGE OF H.M.S. CHALLENGER. 
the openings in the lateral faces of the radials, but close to their inner edges, are well 
shown in Pl. VII. fig. 6a. 
As in the Comatule, therefore, the circular commissure of Bathycrinus (Pl. VIIb. 
fig. 4, cco) is in the innermost part of the radial pentagon, 7.e., quite near its centre. 
There is but a thin layer of limestone between it and the central space, while almost the 
whole of the fibres forming the interradial ligaments are outside it. The length of these 
primary interradial cords and their reception in grooves on the apposed surfaces of 
contiguous radials is very anomalous; and although I detected the true nature of these 
grooves at first sight, it was nevertheless very long before I could get rid of the notion 
that the radial openings on the top of the basal ring (PI. VIa. figs. 12, 13) were those 
of the converging branches of the forked interradial canals, as in other Crinoids ; and it 
was not until after some time that I was able to reconcile the apparently conflicting 
evidence afforded by the study of series of transverse sections on the one hand and of the 
dissected calyx on the other. 
From the facts detailed above, it will be seen that Bathycrinus occupies a some- 
what anomalous position among Neocrinoids. In Comatula, Pentacrinus, Apiocrinus, 
and Hncrinus the primary interradial cords fork within the basals; and the adjacent 
branches of neighbouring forks enter the radials by more or less distinctly double 
openings on their inner or under faces; but in Bathycrinus not only do the cords not 
fork within the basal ring, but they rise through half the height of the radial pentagon 
before doing so (woodcuts, fig. 13, a7; fig. 14). The nearest approach to this condition is 
presented by Rhizocrinus, though the relative proportions of the plates are exactly the 
reverse of what we meet with in Bathycrinus. In fact, if we make allowance for this 
difference the condition of Bathycrinus, except for the presence of the intraradial com- 
missure, is almost exactly that which was described by Ludwig in Rhizocrinus; though, 
as pointed out already, the real condition of this genus is slightly more normal, 7.e., the 
primary cords fork within the basals, and their converging branches enter the inner ends 
of the radials as in other Crinoids. 
The first radials, which form by their apposition a rapidly expanding eup, have an 
elongated, trapezoidal outline and rounded outer surface. According to Sir Wyville 
Thomson,’ those of Bathycrinus aldrichianus are “ often free ; but in old examples they 
also are frequently anchylosed into a funnel-shaped piece.” In all specimens of this type 
which I have seen, however, the radials are united laterally, just as in other Crinoids ; 
though they separate more readily than usual when treated with hot alkalies. The 
ligaments uniting them are close and well defined in the lower part of the funnel (PI. VIIb. 
fig. 4, 7); but in the upper part, 7.e., just below the level of the articular surface, there is 
no interradial ligament (Pl. VIIb. fig. 5), which probably explains the description that 
has just been quoted from Sir Wyville Thomson. The distal articular faces of the radials 
1 Journ. Linn. Soc. Lond. (Zool.), 1876, vol. xiii. p. 50. 
ler ee eT 
wie) 
