A6 FOSSIL ASTEROIDEA. 
rupted regular curve between the adcentral margin of the plate and the margin 
in the lateral wall adjacent to the infero-marginal plates. The height of the 
plates as seen in the lateral view of the disk is greater than their length, and 
there is an apparent increase in height as the plates approach the extremity of 
the ray, the ultimate plate being still higher and distinctly tumid (see Pl. XII, 
fig. 2b). The whole superficies of the plates is covered with small, widely spaced, 
equidistant, uniform punctations; and there is a narrow depressed border sur- 
rounding the margin of the plate with much smaller and closely crowded puncta- 
tions, upon which minute miliary granules were previously borne. 
The ultimate paired plate is much larger than any of the other supero-marginal 
plates, its length as measured on the outer margin being more than twice the 
length of the other supero-marginal plates. Its breadth is about equal to that of 
the adjacent supero-marginal plate. It is subtriangular in form as seen from 
above, and the line of junction with the corresponding companion plate of the 
adjacent side of the disk is complete throughout, and coincides with the median 
radial line. he convexity of the plate falls in a line parallel and adjacent to this 
margin of the plate, and its height is greatest there. From this convexity the 
surface slopes gradually and regularly in conformity to the curve of the superficies 
of the other supero-marginal plates. The actual dimensions of the ultimate plate 
in the example under notice are, length 7 mm., breadth 7 mm.; greatest height as 
seen inthemarginalview, about 8°5 mm. The surface of the ultimate plate is marked 
with a precisely similar ornamentation to that on the other supero-marginal plates. 
The odd terminal plate is very small, and though only traces are present in 
the type it is well preserved in other examples. It is prominent, cylindrical, and 
abruptly truncate, resembling in all respects the form described in Metopaster 
Parkinson. 
The madreporiform body, which is only partially exposed in the example under 
notice, is apparently subtriangular in outline, and is marked with very fine centri- 
fugally radiating striations (see Pl. XII, fig. 2 ¢). 
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 subequal to 
that of the superior series, but their height as seen in the marginal view of the 
disk is much greater, the thickness of the whole margin, 7. e. both series of plates 
together, being 10 mm. in an example whose minor radius is 19mm. _ Four plates 
underlie the superior ultimate plate, the last two being very small and triangular 
inform. All the four are adjacent to the adambulacral series of plates. The 
ornamentation or surface-marking of the infero-marginal plates is precisely 
similar to that of the supero-marginal series. 
