50 FOSSIL ASTEROIDEA. 
The position of the madreporite is nearer the centre of the disk than the 
margin. 
The infero-marginal plates are six in number, counting from the median inter- 
radial line to the extremity,—that is to say, there are twelve for the whole side of 
the disk, as against six in the supero-marginal series. The length of the two 
innermost plates on each side of the median interradial line is subequal to that of 
the superior series, but the four succeeding infero-marginal plates are much shorter, 
and together correspond to the large ultimate supero-marginal plate. As seen in the 
lateral wall of the disk the height of the infero-marginal plates is very little more 
than one-half that of the superior series, the actual proportion in the specimen 
under notice being less than three-fifths. The breadth of the plates adjacent to 
the median interradial line on the actinal surface is 7°5 mm. in an example whose 
major radius measures 25 mm. and the minor radius 20 mm. The breadth of the 
marginal border diminishes so rapidly on each side of the median interradial line 
towards the extremities of the rays that the inner margin of the series of infero- 
marginal plates of each side of the disk is practically a sector of a circle. The 
surface of the plates is marked with small widely spaced punctations, and there is 
a narrow depressed border round the entire margin of the plate which is very finely 
punctate ; the border is broader at the adcentral end of the plate and the adjacent 
corners than elsewhere. 
The adambulacral plates are small, broader than long, and their surface is 
marked with about three oblique series, and an outer irregular group of fine 
punctations upon which the spinelets composing the armature of the plates were 
articulated. There are about six punctations in the innermost ridge or series 
adjacent to the ambulacral furrow. A few spinelets are still preserved in an 
example from the Upper Chalk near Bromley, from which this description is taken, 
which is in the British Museum collection, and bears the registration number, 
“2613.” The spinelets are cylindrical, truncated, and do not appear to taper ; 
and their length is about equal to the length of the plates. 
The actinal intermediate plates are rhomboid and hexagonal or polygonal in 
form, and their surface is entirely covered with small equidistant punctations, 
upon which small uniform granules were previously attached. Remains of this 
eranulation are occasionally to be found preserved in situ, and may be seen in the 
example referred to in the preceding paragraph. Small entrenched pedicellarize 
are occasionally present on the actinal intermediate plates. 
Dimensions.—The example figured on Pl. XIV, fig. 2a, has a major radius of 
36°5 mm. and a minor radius of 27 mm. The length of the side is about 40 mm. 
Another specimen, shown in fig. 1 a on the same plate, is rather larger, the length 
of the side being about 45 mm. Much displacement of the plates has occurred in 
