44 FOSSIL ASTEROIDEA. 
to the ultimate supero-marginal plate. As seen in the lateral wall of the disk the 
height of the infero-marginal plates is slightly greater than that of the supero- 
marginal series. The breadth of these plates adjacent to the median interradial 
line on the actinal surface is 6 mm., or even a little more in an example whose 
major radius measures 37 mm. and the minor radius 27 mm. The breadth of the 
marginal border rapidly diminishes towards the extremity of the ray. The 
surface of the infero-marginal plates is ornamented with extremely small and 
closely crowded punctations, upon which traces of a minute, closely crowded, and 
uniform granulation are preserved here and there. 
The adambulacral plates are small, about twice as broad as long, and their 
surface is traversed by about three ridges, bearing punctures, running parallel to 
the ambulacral furrow, upon which the spinelets composing the adambulacral 
armature were articulated. There were about five or six spinelets in each lineal 
series. 
The mouth-plates are regularly triangular, about twice and a half as long as 
broad, and the two adjacent plates which constitute a pair form together a regular 
rhomboid or lozenge-shaped figure. Their surface is covered with small, crowded, 
rather coarse, irregularly disposed tubercles or granules (see Pl. XV, fig. 2 d). 
The actinal intermediate plates are fairly large, and there is a distinct diminu- 
tion in size towards the outer margin of the disk adjacent to the marginal plates. 
The plates adjacent to the adambulacral plates are pentagonal, but a subhexagonal 
or polygonal form elsewhere is the rule, with comparatively little irregularity. 
The surface of the actinal intermediate plates is entirely covered with very small 
equidistant punctations, upon which a uniform close granulation was previously 
borne. Occasional small excavate pedicellariz are present here and there, the 
lateral fossee being shghtly curved. 
Dimensions.—The type specimen is unfortunately fragmentary, and the radial 
dimensions cannot be given. The length of one side of the disk, measured from 
the tip of one ray to the tip of the adjacent ray, is about 41 mm. ; the breadth of 
the supero-marginal plates adjacent to the median interradial line is 9 mm.; and 
the thickness of the margin is about 12 mm. 
In the fine example preserved in the Museum of Practical Geology, Jermyn 
Street, figured on Pl. XV, fig. 2a, the major radius measures 37 mm., and the 
minor radius 27 mm.; the length of one side of the disk measured about 
42 mm., or probably rather more when complete; the breadth of the infero- 
marginal plates adjacent to the median interradial line is 6 mm.; and the 
thickness of the margin is 8°5 mm. 
Locality and Stratigraphical Position.—The type specimen is stated by Forbes 
