EEPORT ON THE CRINOIDEA. 203 



basals of Penfacrinus decor us tliere is but one central opening, so that the primary cords 

 fork within the basals (PL LVIII. fig. l) as they did in Ajnocrinus. But in PentacrinuH 

 hlakei this opening is widely extended laterally, while in Fentacrinus naresianus, Penta- 

 cnnus alter nicirrus,^ and especially in Pentacrinus wyville-thomsoni (PI. XXI. fig. 7a), 

 it is more or less completely divided into two by a vertical partition. In Pentacrinus 

 nsterius and Metacrinus angulatus, lioth of which, and especially the latter, have large 

 basals with a great development of calcareous network on the upper ends of their inner 

 faces, the opening of the central canal is pretty distinctly double. 



On the upper surface of the basals the openings are, of course, perfectly separate. 

 They are situated on either side of the median ridge, and correspond to similar openings 

 on the under surface of the two contiguous radials which partly rest upon each single 

 basal (PL XIL figs. 11, 14, 22, 25; PL XVIII. figs. 5, 7; PL XX. figs. 2, 3, 6, 9: 

 PL XXI. figs. 6, a, h, c, and 7, h; PL XXVI. fig. 9; PL XXX. figs. 5, 7, 8; PL XXXIII. 

 fig. 5 ; Pi. L. fig. 5). In most specimens of Pentacrinus unjville-thomsoni, as in other 

 Pentacrinidae, removal of the basals exposes the apertures on the lower surface of the 

 radials where the secondary axial cords enter them, together with the lowest portion of 

 tlie central plug (PL XX. fig. 9). But in one individual of Pentacrinus wyville-thomsoni 

 Dr. Carpenter found this plug to be somewhat unusually developed. Its low^er surface 

 forms a tolerably well defined pentagonal plate, the angles of which are interradial in 

 position (PL XX. figs. 4, 5, 6, 8). It lies between the basals and radials, and is pierced 

 in the centre for the passage of the plexiform gland rising out of the chambered organ, 

 together with openings through which the secondary axial cords passed on their way 

 from the basals to the radials, the apertures in the latter plates being entirely concealed 

 by it. 



The radials of Pentacrinus thus difier very considerably from those of Comatula, for 

 the proximal openings of their central canals are really on their dorsal faces, viz., at the 

 central ends of wliat I have called the inner dorsal surface, i.e., that part which rests 

 on the basals (PL XII. figs. 11, 22 ; PL XX. fig. 9 ; PL XXI. figs. Ga, 66, 6c; PL L. 

 fig. 5) ; whereas in the Comatulse, as I have shown elsewhere,^ these openings are on the 

 inner faces of the radials, i.e., those which form the walls of the radial funnel that con- 

 tains the plexiform gland rising from the chambered organ. They are also less closely 

 approximated in Pentacrinus than in Comatula, one being situated on either side of the 

 strong crest which divides the inner dorsal surface into two lateral halves, instead of 

 licing only separated by a very delicate calcareous bar. The converging axial cords 

 which enter these openings on the radials of Pentacrinus (PL XXIV. figs. 7-9 ; 

 PI. LVIII. figs. 1-3 — ar) run upwards and outwards for some little way before they 

 are united by the interradial and intraradial cords to form the circular commissure 



^ I have only seen single specimens of the dissected calyx in these three species. 

 2 Trans. Linn. Soc. Land. (Zool.), ser. 2, vol. ii. p. 78, pis. iv.-vii., 1877. 



