REPORT ON THE CRINOIDEA. 293 
basals of Pentacrinus decorus there is but one central opening, so that the primary cords 
fork within the basals (PI. LVIII. fig. 1) as they did in Apiocrinus. But in Pentacrinus 
blake: this opening is widely extended laterally, while in Pentacrinus naresianus, Penta- 
erinus alternicirrus,' and especially in Pentacrinus wyville-thomsoni (Pl. XXI. fig. 7a), 
it 1s more or less completely divided into two by a vertical partition. In Pentacrinus 
asterius and Metacrinus angulatus, both 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 
basala (ily Nuleshes pbleg ta 225 25); Pho XVI. figs: 95, 7; Pl. XX. figs. 2, 3; 6; 9); 
PEDO hes, 60, 0).¢,and 7,0; Pl. XXVI. fio. 9; Pl) XXX. figs. 5;7,8; Pl XXXL 
fig. 5; Pl. L. fig. 5). In most specimens of Pentacrinus wyville-thomsoni, as in other 
Pentacrinidz, 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 
the 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 lower 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 bemg entirely concealed 
by it. 
The radials of Pentacrinus thus differ 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 what I have called the inner dorsal surface, 7.e., that part which rests 
on the basals (Pl. XII. figs. 11, 22; Pl. XX. fig. 9; Pl. XXI. figs. 6a, 6b, 6c; PI. L. 
fie. 5); whereas in the Comatule, as I have shown elsewhere,’ these openings are on the 
inner faces of the radials, 7.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 
being 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; 
Pl. LVIII. figs. 1-3—ar’) run upwards and outwards for some little way before they 
are united by the imterradial and intraradial cords to form the circular commissure 
1 T have only seen single specimens of the dissected calyx in these three species. 
2 Trans. Linn. Soc. Lond. (Zool.), ser. 2, vol. ii. p. 78, pls. iv.—vii., 1877. 
