212 THE VOYAGE OF H.M.S. CHALLENGER. 



In fact the articular ridge and not tlie 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 Cyathidnim. 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 Cyathidnim ^ as 

 composed " d'une piece centro-dorsale cupuliforme portant, sur son bord superieur, cinq 

 facettes syzy gales, sur lesquels reposaient, sans doute, des pieces 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 suj^poses, though their inferior 

 boundary is still uncertain. 



The inner 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 (PI. X. figs. 1, 4, vrf; 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 Cyathidium 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 -nath 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 ligament. 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. 

 Loven. "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 



^ Pal^ont. Fran^., Inc. cit., p. 187. 



2 AstyliJe Crinoideii, loc. cit., pp. 50-54, Taf. iii. figs. 11-15. 



