282 THE VOYAGE OF H.M.S. CHALLENGER. 
and a few in the central region bear spines, whereas in the present form all are normally 
so furnished. On the actinal surface also the spines are similarly more numerous in 
Calliaster baccatus. The adambulacral armature in the two forms is strikingly different ; 
in Calliaster childreni the furrow series of spinelets being seven or eight in number, 
very small and equal; but in the present form there are three only, which are large and 
unequal. Other differences occur in minor points of ornamentation, &c., to which it 
is unnecessary to refer in detail. 
Genus Chitonaster, Sladen. 
Chitonaster, Sladen in Narr. Chall. Exp., 1885, vol. i. p. 614. 
Marginal contour stellate, with a rigid convex disk, and short, tapering, rounded rays. 
Abactinal area high and inflated over the disk. 
Abactinal area covered with closely-fitting hexagonal, or slightly rounded, plates 
overlaid with a uniform layer of membrane. Lach bearing a short obtuse spinelet or 
elongate tubercle. 
Marginal plates large and covered with membrane. ‘The superior and inferior series 
subequal, the latter being rather broader. The supero-marginal plates normally bear 
two short, obtuse, cylindrical spinelets, standing one above the other on the median 
transverse line of the plate. The infero-marginal plates are similar in form and character, 
and each bears two or three similar spinelets, also arranged in line transverse to the axis 
of the ray. 
Adambulacral armature consisting of three large, isolated, cylindrical, obtuse spinelets, 
which form a line at right angles to the furrow. 
Actinal intermediate areas small, confined to the region of the disk, and accommodating 
very few intermediate plates. 
Madreporiform body small, situated nearer the margin than the centre of the disk. 
Anal aperture subcentral. 
No pedicellarize present. 
Remarks.—This genus is distinct from all known forms, and is remarkable not only 
for its structure, but also on account of the great depth at which it occurs. The general 
form and the character of the plating appear to justify the inclusion of Chztonaster in the 
Pentagonasteridz, notwithstanding the fact that the family contains no genus with which 
a direct alliance can be established. This circumstance is, however, not so surprising as 
would at first appear, when it is borne in mind how very few members of the Penta- 
gonasteridze occur in deep water. 
Unfortunately only a single example of this interesting starfish was collected by the 
Challenger: the following remarks are therefore necessarily limited entirely to external 
characters, as I consider it undesirable to mutilate this unique specimen. 
