212 THE VOYAGE OF H.M.S. CHALLENGER. 
In fact the articular ridge and not the edges of the muscle-plates forms the immediate 
boundary of the central cavity; and the fossa for the dorsal ligament is still more 
reduced than in Holopus, where it is represented by a median pit that is scarcely to be 
traced at all in Cyathidium. The presence of these articular faces seems to have 
escaped the notice of de Loriol, which is doubtless due to his not having been able to 
examine sufficiently good specimens. For he describes the calyx of Cyathidium* as 
composed “dune piéce centro-dorsale cupuliforme portant, sur son bord supérieur, cing 
facettes syzygales, sur lesquels reposaient, sans doute, des piéces radiales dont le nombre 
est inconnu.” These supposed syzygial facets are, however, the articular faces of first 
radials, which are by no means so unknown as de Loriol supposes, though their inferior 
boundary is still uncertain. 
The imner face of each side of the more or less pentagonal cup formed by these 
radials is marked by a median furrow corresponding to the ventral radial furrow of other 
Crinoids (Pl. X. figs. 1, 4, orf; Pl. XX. fig. 8), and immediately external to its upper 
end is the opening of the central canal. These features indicate that in Steenstrup’s 
Cyathidium the sides of the pentagonal cup correspond to the radials, just as they do in 
Holopus (Pl. V. figs. 1, 2, 4). To this same genus Cyathidium, Schliiter has doubtfully 
referred a minute Crinoidal calyx discovered by him in the Eocene of Monte Spilecco 
near Venice.” It only reaches 9 mm. in height, but has the same general form as the 
cup of the recent Holopus, being attached by a spreading base, between which and the 
cup proper there is a more or less well marked constriction. This does not appear to be 
generally the case in the Faxoe specimens. In one or two cases there seem to be traces 
of basiradial and interradial sutures, and the position of the former, if real, would indicate 
that the basals are relatively much higher than they can possibly be in Holopus. 
The great peculiarity of Cyathidiwm spileccense, however, lies in the relative position 
of the radials in the pentagonal cup. Their articular surfaces correspond with the angles 
of the pentagon, and not with its sides, as is the case both in Holopus and in Steenstrup’s 
Cyathidium, while the middle of each side is raised into a slight ridge which separates 
the articular facets of two contiguous radials. The result of this is that the five openings 
of the radial canals are situated at the angles of the calyx. They occupy about the middle 
of the rim, the outer edge of which is slightly truncated, and shows traces of a fossa for an 
elastic hgament. The peculiar semilunar shape of these articular facets is considered by 
Zittel as one of the generic characters of Cyathidium. But it certainly does not appear 
in any of the Faxoe specimens which were lent to Sir Wyville Thomson by Prof. 
Lovén. We know too little about both of these species to make them types of 
different genera; and in default of further information it appears undesirable to unite 
them with Holopus. Both forms resemble and differ from it in various points, and are 
1 Paléont. Frang., loc. cit., p. 187. 
* Astylide Crinoiden, loc. cit., pp. 50-54, Taf. iii. figs. 11-15. 
