﻿10 FOSSIL ASTEROIDEA. 



The supero-marginal plates are about twenty-eight in number, counting from 

 the median interradial line to the extremity. (This number is taken from the 

 fragment figured on PL VII, fig. 4 a ; in the larger example drawn on PI. V, 

 fig. 2 a, twenty-two may be counted up to the place where the ray is broken.) 

 They form a well-defined, conspicuous border, but the breadth of this is distinctly 

 less in proportion to the size of the disk when compared with the breadth of the 

 marginal plates in Galliderma Smithiae. The largest supero-marginal plates in the 

 specimen figured on PI. V, fig. 2 a, near the median interradial line, measure 5'25 mm. 

 in breadth and 3'25 mm. in length. The breadth diminishes very slightly as 

 the plates approach the base of the ray, but from that part outward the length of 

 the plates becomes much reduced — the breadth remaining the greater dimension 

 throughout the ray. 



The supero-marginal plates are comparatively flat on the abactinal surface and 

 only slightly depressed along their margins of juncture. The general surface of 

 the whole series has the character of sloping at a small angle to the margin of the 

 disk, to which it gives a slightly bevelled appearance. The marginal surface of 

 the plate is almost vertical, the junction of the abactinal and marginal surfaces is 

 well rounded but not tumid, and there is very slight, if any, convexity on the 

 marginal surface, at least along the disk. The height of the plates as seen in the 

 margin is only a little greater than the length, and the diminution in height is 

 only very trifling as the plates proceed along the ray. The whole superficies of 

 the plates is covered with small hexagonal punctations upon which granules were 

 previously borne. Small foraminate pedicellame are occasionally present here 

 and there upon the plates ; the foramen is small and oval, and is surrounded by a 

 definite margin or lip. Sometimes more than one are present on one plate. 

 The example figured on PI. VII, fig. 4 a, is remarkable for the presence of the 

 prominent teat-like eminences, in the centre of which the pedicellarian foramen is 

 situated. These eminences at first sight look like tubercles for the articulation of 

 spines (see PL VII, figs. 4 a, 4 c). A similar character is also seen in the example 

 drawn on PL V, fig. 2 a, but is less strongly marked (see fig. 2 d). 



The abactinal area of the disk is covered with small, regular, hexagonal and 

 tetragonal plates or paxillar tabula ; those in the radial areas being regularly 

 hexagonal and larger than those in the intermediate regions, which are rhomboid, 

 and all diminish in size as they approach the margin. The abactinal plates or 

 paxillse do not appear to extend beyond the twelfth supero-marginal plate, counting 

 from the median interradial line ; the supero-marginal plates of the two sides of 

 the ray meeting in the median radial line beyond this point. The plates or paxillse 

 of the median radial series are larger and broader than any of the others ; they 

 are succeeded on each side by five or six longitudinal series of hexagonal plates, 

 those of the second or third series from the median series measuring about l"5mm. 



