REPORT ON THE CRINOIDEA. 125 



the basals and enter two adjacent radials (PL XXIV. figs. 7-9; PL LVIIL figs. 2, .3, ar) 

 There are thus two apertures on the upper surface of each basaL and two on the under 

 surface of each radial (PL XIL figs. 11, 14, 22, 25; PL XVIII. figs. 5, 7; PL XX. figs. 2, 

 3, 6, 9 ; PL XXI. figs. 6a, 6b, 6c, 7a, 7h ; PL XXX. fig. 5, 7, 8 ; PL L. fig. 5). As the 

 two cords which enter each radial converge towards its distal surface, each of thena is 

 joined laterally by a commissure to its fellow in the next radial which springs from the 

 same primary trunk as itself These lateral branches form the interradial, and by far the 

 larger portions of a circular commissure which unites the five pairs of cords within the 

 radials (PL XXIV. fig. 9, c.co ; PL LXII.) ; while the two converging cords within the 

 substance of each radial are also united by a very short intraradial commissure (PL XXIV. 

 fig. 9, i.co). 



This circular commissure occupies a canal which traverses the radials from side to 

 side, lying in the Comatulse very close to their distal face, but more centrally in the 

 Pentacrinidse. Its openings on the lateral faces of the radials are shown in PL XIL 

 figs. 11, 22 ; PL XX. fig. 6 ; PL XXL figs. 6a, 6h, 6c ; PL XXX. figs. 5, 8. 



The two secondary cords within the basals and the proximal parts of the radials of 

 Pcntacrinus are more widely separated than the corresponding structures in the Comatulse 

 (PL XXIV. figs. 7, 9 ; PL LVIIL figs. 1, 2 — ar), so that the intraradial commissure is 

 better defined (PL XXIV. fig. 9, i.co). Beyond the circular commissure the two axial 

 cords of each ray lie very close together, though still distinct, just as in the Comatula3. 

 Each of them forks in the axillary, and there is the same horizontal commissure as was 

 described by Ludwig in Antedon rosacea. 



So far as the fossil Neocrinoids are concerned, Encrinus and Apiocrinus seem to have 

 had an arrangement of the axial cords essentially similar to that prevailing in the 

 Pentacrinidae and Comatulse. In the former genus, as already pointed out by Ludwig, 

 no canals have been described either for the intraradial commissure or for the horizontal 

 commissure in the axillary ; while the secondary radial cords remain distinct as far as 

 the axillaries, even to the extent of being lodged within separate canals in the second as 

 well as in the first radials. The double canals are continued through the whole length 

 of the arms ; and in some species these consist, after the base, of a double row of joints, 

 each of which is pierced at its inner end by the two canals. The absence of any canals 

 which could lodge an intraradial commissure is very singular ; and it is also remarkable 

 that the interradial portions of the circular canal should lie so completely in the distal 

 parts of the radials. They only join the axial canals where these open on the distal 

 faces of the radials ; so that if an intraradial commissure were present at all, it must have 

 lain just at the edge of the first radials, almost among the ligamentous bundles uniting 

 them to the following joints. 



The axial cords of Encrinus were lodged in canals throughout their whole length, 

 those within the basals occupying grooves within the substance of the plates which were 



