228 THE VOYAGE OF H.M.S. CHALLENGEE. 



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 fossse 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 

 (PI. 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 

 fossae 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 

 (PI. XII. figs. 11, 22 ; PL XX. fig. 9 ; PI. L. fig. 5). They are usuaUy quite smaU 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 corresjDondiug openings in the 

 fossae on the upper surface of the basal ring (PL Vila, 

 figs. 12, 13). Although the fibres of the basiradial 

 ligament are generally distriljuted 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 Vllb. fig. 3, which passes rather 



f 10. 12. — DiaOTam of a horizontal section , , i • i i j_i i j_i i i r , i 



tiirough tiie calyx of Bathycrinus aidric abovc their Icvel turougli the general plane 01 the 



hianus, at the level of the upper part of the • i • i ■ i i i 



basiradial suture ; x 45. ai, primary inter- S\T10StOSlS ; DUt lU tUC UCXt SCCtlOU tUCy are Clcaiiy 

 radial cords ; I, parts of the basiradial •' iivi i ■ ^ 



ligament ; L, interradial ligament uniting ftl, visible, CUt SOmCwhat obliquch^ aS shoWU lU the WOodcUt 

 the first radials ; x, plexiform gland. 



(fig. 12, 1). Both in the woodcut, and in PL Vllb. fig. 3, 

 the axial cords {ai) 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. Q>a). 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 Comatulae and Pentacrinidse (PL XXIV. fig. 9, ceo). This is also the 



