690 
Proceedings of the Royal Irish Academy. 
The mouth-plates are elongate and triangular, but not conspicuous. 
Their armature consists of a marginal series of nine or ten short, equal 
spinelets, similar to those in the furrow series on the adambulacral 
plates, but with a tendency to become more distinctly prismatic as 
they proceed inward ; a series of six to eight large, low, coarse and 
distinctly prismatic granules, forming a longitudinal series on the 
actinal surface of the plate parallel to the suture which unites the 
two mouth-plates of an angle ; and an intermediate series between 
these two series of about three similar prismatic granules. 
The actinal interradial areas are paved with rather large sub- 
rhomboid intermediate plates, arranged in series parallel to the ambu- 
lacral furrows. The surface of the plates is covered with rather large, 
low, uniform, distinctly-spaced, hemispherical granules, which are 
arranged in straight series along the margins of the plates, but show 
no definite order within this boundary. 
The anal orifice is sub-central, and on the right posterior side of a 
plate larger than those in the immediate neighbourhood. 
The madreporiform body, which is small and polygonal in outline, 
is situated at about one-third of the distance between the centre and 
the margin. The surface is marked with rather course irregular 
convolutions. On its adcentral side is a single large basal plate, larger 
than the madreporite itself ; and a similar large basal plate is present 
in each of the other interradial areas in a corresponding position, and 
larger than any of the other abactinal plates. 
Colour in alcohol, a bleached yellowish white. 
Locality.— L^t. 51° V N". ; Long. 11° 50' W. Depth 750 fathoms. 
RemarTcs. — This species has more distinctly lunate sides, and 
more obtusely-rounded radial angles than Pentagonaster granularis^ 
E-etz., sp., to which at first sight it presents some resemblance. It 
is at once distinguished, however, by the great width of the marginal 
plates, which are much broader than long, by the complete granula- 
tion of the marginal plates, by the armature of the adambulacral 
plates, which has more spines in the furrow series, and a greater 
number of series on the actinal surface of the plate. Pedicellaria^ 
are also more numerous and more distinctly entrenched. 
8. Pentagonaster concinnus, n. sp. (Plate xxvi., figs. 1-5.) 
Eays five. E = 22 mm. ; r = 12 mm. ; E = 1-83 r. The 
minor radius is thus in the proportion of 54*5 per cent. 
General form fiat, and rather thin. Marginal contour a deeply 
