34 FOSSIL ASTEROIDEA. 
The abactinal area of the disk within the boundary of the marginal plates is 
covered with small sub-regular plates or paxillar tabulez, an hexagonal form pre- 
dominating especially in the radial regions ; and a small but distinct diminution in 
size takes place as the plates approach the margin of the disk. All the plates 
have their surface marked with minute, shallow, and closely placed punctations— 
the impressions of the attachment of the granules previously present. The 
primary basal plates are larger than any of the other abactinal plates, and they 
are well shown in several of the drawings illustrative of this species (see Pl. X, 
figs. 1, 2a). Occasional plates bear small entrenched pedicellariz, the normal 
form consisting of a small, central, ipped foramen with a lateral trench on each 
side. It frequently happens, however, that the organ exhibits a more complex 
development, and assumes a stellate form in consequence of the presence of addi- 
tional trenches—five or six being not an unusual number—which radiate from the 
central foramen ; the whole being placed on a small hemispherical elevation, and 
producing an appearance shown on Pl. X, fig. 2 d. 
The madreporiform body is large and subtriangular in outline; and its surface 
is sculptured by very fine striations which radiate from the centre to the margin, 
with more or less wavy lines here and there (see Pl. X, fig. 2c). The margin 
of the plate is surrounded by three large plates, one on the adcentral side of 
the madreporite towards which it presents a straight suture; the other two 
plates are on the remaining sides of the triangular body, and they have a 
concave curve directed towards the madreporite to correspond with the 
convexity of its sides. The position of the madreporite is nearer the centre of 
the disk than the margin. 
The infero-marginal plates are seven in number, counting from the median 
interradial line to the extremity—that is to say, there are fourteen for the whole 
side of the disk, as against eight in the supero-marginal series. The length of 
the three innermost plates on each side of the median interradial line is equal to 
that of the superior series, but there are four infero-marginal plates corresponding 
to the large ultimate supero-marginal. As seen in the lateral wall of the disk the 
height of the infero-marginal plates is less than that of the supero-marginal series. 
The breadth of these plates adjacent to the median interradial line on the actinal 
surface is 7°5 mm. in an example whose major radius measures 36°5 mm. and the 
minor radius 27°5 mm. The breadth of the marginal border rapidly diminishes 
towards the extremity of the ray. The surface of the plates is ornamented in a 
precisely similar manner to that of the supero-marginal plates. A narrow border 
of smaller granulation is also present round the whole margin of the plate, 
similar in all respects to that already described in the case of the superior 
series of plates. 
The adambulacral plates are small, about or nearly twice as broad as long, and 
