EEPORT ON THE CEINOIDEA. 201 



bounded by these Hues, tlie whole of the skeleton is formed by the regular, small-meshed 

 network ; while the inner, less dense portion which has a whiter look, narrows gradually 

 downwards as shown in fig. 3, until it entirely disappears from the wall of the diminish- 

 ing central funnel. There is no trace of it round the greatly reduced opening on the 

 under surface of the segment of the cup which is represented in figs. 3 and 4. In this 

 specimen, as in that represented in PL I. and also in d'Orbigny's original, the lowest 

 portion of the calyx-tube immediately above the spreading base, is partially covered with 

 a chitinous-looking layer of variable height, and marked by roughly concentric lines 

 which somewhat obscure the calcareous network beneath. It is merely a thin superficial 

 skin, however, and is evidently of no special importance, or it would be universally 

 present. 



The pentagonal figure indicating the position of the articular ridges on the radials is 

 still visible in the section shown in fig. 4, which corresponds to the upper surface of the 

 fragment represented in fig. 3 ; and the openings of the central canals are also traceable. 

 This would indicate that the greater part of the calyx-tube is composed of elongated 

 radials. One of these canals is seen in nearly longitudinal section in the portion of the 

 lower half of the cup which has been removed to expose the view given in fig. 3. But it 

 is not traceable beyond the limit of the whiter, less dense portion of the skeleton. I 

 strongly suspect, therefore, that this indicates the position of the lower surface of the 

 radials ; and the analogy of all other Crinoids would lead to the conclusion that the 

 small portion of the calyx-tube between this and the spreading base consists of closely 

 anchylosed basal plates, the presence of which was taken for granted by Sir Wyville 

 Thomson.^ There must certainly be a chambered organ, from the fibrillar envelope of 

 which the axial cords of the rays and arms originate (PI. Vc. fig. 2, A) ; and one would 

 naturally expect it to be situated at the lowest part of the calyx-tube. This narrows 

 rapidly downwards, and its interior is marked by five vertical ridges corresponding with 

 the radials in position. They are fairly distinct at the level of the section shown in 

 PL V. fig. 4 ; but they become less marked as they proceed downwards, and, being 

 composed of the whiter, less dense network, disappear together with it. They extend 

 upwards to the edge of the cup at the intermuscular notches ; though they are much less 

 distinct on some of the radials than on the others. They thus occupy the position of the 

 ventral radial furrows which are often so marked on the interior of the central funnel of 

 the calyx in other Crinoids (PL X. figs. 1, 4, vrf; PL XII. fig. 15 ; PL XX. fig. 8 ; 

 PL XXX. fig. 3). 



From the facts detailed above, we may, I think, assume with tolerable certainty that 

 the tubular body-chamber of Holopus is not composed of a " piece centro-dorsale sessile " 

 as stated by de Loriol ;" but that it consists of basals and radials like the calyx of any 

 other Crinoid. I cannot quite make out whether de Loriol employs the word " centro- 



1 hoc. cit., p. 407. - Palcont, Frang., he. cit., p. 188. 



(ZOOL. OHALL. EXP. PART XXXIl . 1884.) 11 26 



