336 THE VOYAGE OF H.M.S. CHALLENGER. 
of a pedicle with a slightly expanded base and a rounded clavate extremity, on which the 
spinelets that form the crown are articulated. The expansion of the base of the paxillz 
is very slight, subcircular, or irregular in outline, and usually exhibiting two or three 
faint prolongations. The bases of the paxillee are closely placed, and occasionally a trace 
of overlapping may be found here and there. This structure is identical with that met 
with in the Astropectinids, and has hitherto been looked upon as specially characteristic 
of that group. 
The adambulacral plates, their armature, and the mouth-plates have strictly the 
characters of the Pentagonasteride. The marginal plates are likewise suggestive of 
the same group, and, notwithstanding their inequality and insignificant development, 
approach the habit of such forms as Gnathaster paxillosus, Gray, sp., from which also 
the general outline of the body of Mimaster tizardi is not far removed. 
The actinal intermediate plates recall in their character the intermediate plates of 
the Asterinidee, whilst their arrangement also approaches in a certain degree that of some 
of the Pentagonasteride. 
2. Mimaster cognatus, n. sp. (Pl. XLVI. figs. 3 and 4; Pl. LXII. figs. 4 and 5). 
Rays five. R=63-65 mm.; r=21°5 mm. R=3 r. Breadth of a ray near the 
base, between the third and fourth infero-marginal plates, 20 mm. | 
General form stellato-pentagonal. Rays moderately produced, broad at the base and 
tapering gradually to the extremity, which is slightly upturned. Abactinal area more or 
less inflated, causing a puffy appearance over the disk and an irregular subcylindrical form 
to the rays. Actinal area subplane, but with a tendency to become convex along the ray. 
Interbrachial ares wide and subacute. 
The abactinal area is covered with a great number of small paxille, which show an 
obliquely transverse arrangement at the sides of the ray, especially distinct near the base, 
but are irregular in their disposition in the central region of the disk, along the median 
line of the ray, and at the extremity. The regularly disposed paxille are larger than the 
others, and all gradually diminish in size as they approach the extremity of the ray, where 
they become almost microscopic. The paxillze consist of a delicate pedicle, which expands 
considerably at the distal extremity, and is surmounted by a crown of numerous delicate 
spinelets, which radiate more or less, and produce a tufted form of paxilla. The papule 
are comparatively large. 
The marginal plates are small and confined to the lateral and actinal surfaces. The 
supero-marginal series are inconspicuous and scarcely distinguishable from the paxille of 
the abactinal area; in fact, they are unnoticeable when the starfish is viewed from above. 
The infero-marginal plates, which are about thirty-six in number, counting from the median 
interradial line to the extremity, are comparatively large and well developed, forming a 
