268 
THE YOYAGE OF H.M.S. CHALLENGER. 
Calcareous ring of ten simple pieces, devoid of prolongations posteriorly ; tlie 
interradial carry anteriorly one point, the broad radial have four. 
Habitat . — (?). 
Genus Eueyelus, Lampert, 1885. 
Tentacles twenty, in two crowns, each crown composed of ten equal tentacles ; those 
of the inner crown smaller and radial in position, those of the , outer crown larger 
and interradial. Pedicels equally distributed all over the body. Calcareous 
ring like that in Thyone chilensis, composed of ,only five simple pieces, devoid of 
prolongations posteriorly. 
Mucyclus dupUcatus, Lamport; 1885. 
Body ovate, slightly curved. Deposits — sparsely scattered, small, tuberculated rods, 
slightly enlarged and usually perforated at each end, thus resembling those in 
Thyone chilensis. 
Habitat. — Callao, Peru (Lampert). 
A detailed comparison of the descriptions ,of Mucyclus dupUcatus and Thyone chilensis 
clearly shows that the two forms are very nearly related, and that the only 
points of distinction are the number and arrangement of the tentacles. 
Supposing that Semper is right in stating the number of tentacles to be ten in 
,his Thyone chilensis, it remains unexplained how it is possible that species of 
two different genera, which also belong to different subfamilies, can be developed 
an “every detail” like one another. For my own part I am very much tempted 
to think that Semper has made a mistake in conuting the tentacles, in which 
case the two forms will be identical, but if he be right, there is still weighty 
reason for placing the two forms side by side, in spite of the differences in the 
number of tentacles, because they present the most obvious similarity in every 
other respect. I fear that the individual variations in regard to the tentacles in 
many Dendrochirotes may be much more extensive than has been hitherto 
supposed, and that this variatiqn principally takes place in the “ polychirote ” 
Dendrochirotes. In all those Dendrochirotes, ,on the contrary, which are 
characterised by possessing only ten tentacles, these Appear to be almost constant 
in number, size, and position. From deficient knowledge in these respects it 
.does not seem very suitable at present to found the subfamilies above mentioned 
merely on the differences in the tentacles. 
Lampert has associated with the following three forms, incompletely described by 
Eathbun, Anderson and Barrois, the names of their respective discoverers.: — 
Holothuria rathbunii, Lampert, 1%%^ = Holothuria, sp. mihi, p. 239. 
Colochirus andersoni, Lampert, =. Holothuria, sp. mihi, p. 240. 
.Semperia barroisi, Lampert, 1885 = Thyone fusus, mihi, p. 134. 
