58 THE VOYAGE OF H.M.S. CHALLENGER. 
five. Their arrangement is not very recular, but appears normally to fall into two longi- 
tudinal series of three each; the central pair being wider apart than the others. 
The madreporiform body, which is situated midway between the centre of the disk 
and the margin, is small and circular, but is convex and conspicuous, and with its 
surface grooved with rather coarse striation furrows, which have rather a reticulate 
appearance. 
Colour in alcohol, ashy white, with a yellowish or ochre shade along the ray. 
Locality.—Station 205. West of the Island of Luzon (Philippines). November 13, 
1874. Lat. 16° 42’ 0” N., long. 119° 22’ 0” E. Depth 1050 fathoms. Blue mud. 
Bottom temperature 37°-0 Fahr. ; surface temperature 82°-0 Fahr. 
Remarks.—This is an elegant and well marked little form; and Pontaster trullipes 
is readily distinguished from the other species known, by the small and simple paxilla, 
without a central spine; by the absence of actinal intermediate plates ; and by the presence 
of the large isolated pedicellarize only in the interradial lines. In addition to these 
features the posture of the adambulacral armature is in a marked degree characteristic. 
12. Pontaster subtuberculatus, n. sp. (Pl. V. figs. 3 and 4; Pl. XIII. figs. 7 and 8). 
Rays five. R= 24-25 mm.; r=7'5 mm. R= 3'25r. Breadth of a ray near the 
base, 7 mm. 
Rays rather short, broad at the base, and tapering continuously to the extremity, 
which is comparatively broad and obtuse. Interbrachial arcs well rounded. Abactinal 
surface flat, sloping slightly to the extremities of the rays. ‘The paxillar area slightly de- 
pressed below the level of the marginal plates. Actinal surface flat and level. 
The paxille of the abactinal area are small and low, but very distinctly spaced ; their 
crown consists of a group of eight to sixteen small, short, uniform, papilliform granules or 
spinelets, of which from three to five are central and surrounded by the others, but none 
are longer or more prominent than the rest. On the outer half of the rays the paxillz 
have not more than three to five spinelets in each. In each interradial line, midway 
between the centre and the margin, there is a paxilla about twice the size of any of the 
others; and these are probably the representatives of the primary basal plates of the 
embryo. No definite order is observable in the general arrangement of the paxille, and 
no pedicellaris: are present. 
The supero-marginal plates form a broad and slightly raised border on the abactinal 
surface, the intermediate paxillar area midway on the ray being very little broader than 
the marginal plates, and the breadth of the latter diminishes towards the extremity, whilst 
the diminution in the breadth of the paxillar area along the greater portion of the ray is 
comparatively slight. The supero-marginal plates are seventeen in number from the 
median interradial line to the extremity ; their breadth is greater than their length, and 
