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 PI. VII. fig. 6a. 



As in the Comatulse, therefore, the circular commissure of Bathycrinus (PI. Vllb. 

 fig. 4, ceo) is in the innermost part of the radial pentagon, i.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 formina: the interradial lisfaments 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 tojj of the basal ring (PL Vila. 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 Bathycrhms occupies a some- 

 what anomalous position among Neocrinoids. In Comatula, Pentacrinus, Apiocrinus, 

 and Encrinus 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, ai ; 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 

 difi"erence 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, i.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 cup, 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 (PL Vllb. 

 fig. 4, I); but in the upper part, i.e., just below the level of the articular surface, there is 

 no interradial ligament (PL Vllb. fig. 5), which probably explains the description that 

 has just been quoted from Sir Wyville Thomson. The distal articular faces of the radials 



' Journ. Linn. Soc. Lond. (Zool.), 1876, vol. xiii. p. 50. 



