METOPASTER UNCATUS. AQ 
outer margin and rises abruptly from a level area which occupies the inner half of 
the plate along the margin touching the corresponding plate of the adjacent ray, 
—the line of junction of the two plates coinciding with the median radial line. 
The length of the ultimate plate is nearly twice that of the other marginal plates, 
measuring 9°25 mm. in an example whose major radius is 36°5 mm. and minor 
radius 27 mm. As seen in the marginal view of the test, the ultimate is not 
higher or more tumid than the other marginal plates (see Pl. XIV, fig. 2b). The 
outer margin of the ultimate plate has a slight concave curvature, and the inner 
margin adjacent to the corresponding plate is curved convexly towards the 
proximal end of the plate. In consequence of this rounding the two ultimate 
plates in a pair do not unite throughout their entire length, but are separated by 
a small notch at the end of the suture adjacent to the abactinal paxillar area of 
the disk. On the small level area of the ultimate plate are a number of small 
irregular tubercular eminences ; four or five larger than the others form a sort of 
series parallel to the rounded margin, and a longitudinal series of eight or nine 
much smaller miliary granules run along the flank of the longitudinal tumidity of 
the plate; and several additional granules of intermediate size may be present in 
the space between the two series just described. Excepting these granules, the 
surface of the ultimate plate is smooth like that of the other supero-marginal plates. 
The abactinal area of the disk within the boundary of the marginal plates is 
covered with small subregular plates or paxillar tabule, an hexagonal form predomi- 
nating. The plates in the median interradial areas are much larger than the other 
plates on the disk, and a marked diminution in size in all the plates takes place as 
they approach the margin. All the plates have their surface marked with a very 
fine granulation. Small entrenched pedicellaria are occasionally present, but 
there appear to have been very few. 
The primary basal plates are larger than any of the other abactinal plates. 
They are well seen in an example from the Upper Chalk of Kent, in which the 
inner side of the abactinal wall is exposed by the removal of the actinal floor and 
ambulacral plates. This specimen, which is preserved in the British Museum, and 
bears the registration number ‘ 35,496,” is drawn on Pl. XI, fig. 3a. The 
example in question is further interesting in showing that the plates of the radial 
regions have stellate bases, whereas the larger plates of the interradial regions are 
sharply hexagonal, and fit closely to their adjacent plates (see fig. 3). 
The madreporiform body is very small, and is subsagittiform or irregularly 
lozenge-shaped in outline; in the example under notice it is embedded, all except 
two straight sides, in one large adcentrally placed basal plate (see Pl. XIV, 
fig. 2d); the two straight sides are bounded each by one large plate. The 
surface of the madreporite is sculptured by very fine striations, which though 
more or less wavy are directed subparallel to the adcentral sides of the body. 
