140 THE VOYAGE OF H.M.S. CHALLENGER. 
with five spines, and by the clavate spinelets of the disk. This species is especially 
remarkable for the length of the tubular epiproctal prolongation or anal funnel. 
3. Porcellanaster tuberosus, Sladen (Pl. XXIII. figs. 1-4; Pl. XXVII. figs. 13-16). 
Porcellanaster tuberosus, Sladen, 1883, Journ. Linn. Soe. Lond. (Zool.), vol. xvii. p. 223. 
Rays five. R=185mm.; r=6mm. R=8r. 
The rays spring gradually from the angles of the disk and taper moderately towards 
the extremity, maintaining a robust character throughout; the minor radius is in the 
proportion of 32 per cent. The disk is not high, and very slightly inflated. The 
interbrachial arcs are well rounded. 
The abactinal area is covered with a rather fleshy integument beset with simple 
spinelets somewhat closely placed; these are short, cylindrical, obtuse, covered with 
membrane, and occupy the whole of the surface excepting only the extreme angle 
at the base of the ray. A well-developed epiproctal tubular prolongation rises from 
the centre of the abactinal area, and is nearly equal in length to the distance between 
the centre and the inner edge of the marginal plates in the interbrachial are; it tapers 
very slightly towards its extremity, and is indurated with spicular spinelets like the 
rest of the abactinal membrane. 
The marginal plates form a deep margin and curve over roundly in the interbrachial 
ares, the inferior as well as the superior series being visible from above. Upon the 
rays the superior series arch well over and almost meet in the median dorsal line, giving 
to the ray a more or less subcarinate character. The supero-marginal plates are four 
in number from the median interradial line to the extremity, exclusive of the large 
terminal plate, and all are distinctly longer than high. The second and third supero- 
marginal plates from the median interradial line bear short, conical, upright spinelets ; 
but all the rest are unarmed excepting the terminal plate, which carries three spines—one 
at the extremity in the median line of the ray, and one on each side at the anterior 
extremity of the inferior margin of the plate. The terminal plate is swollen and 
prominently tubercular abactinally, and is excavated on its outer extremity for the 
passage of the terminal ambulacral tube. In one ray of the specimen under notice, 
the penultimate supero-marginal plates are also swollen and ankylosed in such a manner 
as to resemble the terminal plate, and bear a single spinelet. 
The infero-marginal plates, which are five in number, are much shallower than the 
superior series, and also shorter. The two series consequently do not correspond, a result 
probably brought about by the extreme development of the terminal plate, which occupies 
the space of both superior and inferior plate. 
One cribriform organ is present in each interbrachial are ; it is rather broad and has a 
deep depression down the median line. The structure is lamelliform. (See Pl, XXVIL.) 
