﻿20 FOSSIL ASTEROIDEA. 



disk. There are only three (or possibly four) supero-marginal plates between the 

 median interradial line and the base of the ray — that is to say, about six plates on 

 each side of the disk. The fourth (or perhaps the fifth) plate counting from the 

 median interradial line, and all the succeeding plates along the ray, appear 

 normally to meet the corresponding plate of the opposite side of the ray in the 

 median radial line. The abactinal surface of the ray is thus occupied entirely by 

 the supero-marginal plates throughout its length. In one of the rays preserved 

 there appear, however, to be traces of a few abactinal plates which interfere with 

 the union of the supero-marginal plates in the median radial line near the base of 

 the ray. As to how far this is normal I am unable to say. 



All the supero-marginal plates are comparatively low and flat. The plates on 

 each side of the median interradial line are 3*5 mm. in breadth, and from 3 to 

 3*5 mm. in length, and are thus practically square. Their abactinal surface is 

 slightly convex ; and their height as seen in the margin is less than the length, 

 and the abactinal surface is gradually bevelled to the inferior margin which abuts 

 upon the infero-marginal plates. The other plates which form the border of the 

 disk-area are of the same size and character as those adjacent to the median inter- 

 radial line. The supero-marginal plates along the ray have the breadth greater 

 than the length, the fifth plate counting from the median interradial line 

 measuring about 3'75 mm. in breadth and 2'5 mm. in length. Their character is 

 similar to that of the plates above described. The surface of the plates is covered 

 with small well-spaced punctations, and there is a distinct smooth border on the 

 inner and two lateral margins of each plate on which no punctations or pits are 

 present. 



Large trench -like pedicellariaa, which are nearly the length of the plate, are 

 present in this species ; they occur more frequently on the infero-marginal plates 

 than on those of the superior series ; in fact, only one or two are present on the 

 latter series of plates in the example under description. 



No other portions of this fragment are available for description. 



Dimensions. — The fragment figured in PI. VIII, fig. 3 a, has a minor radius of 

 about 15 mm. The longest portion of the major radius preserved is about 

 33 mm., and the ray is broken off" abruptly. The thickness of the margin is 

 between 4 and 5 mm. The breadth of the ray at the base is about 8 mm. 



Locality and Stratigraphical Position- — The fragment described, which is, 

 unfortunately, all that I have seen, is from the Upper Chalk of Bromley. It is 

 preserved in the British Museum, and bears the registration number 40,178. 



Remarks. — The character of the marginal plates, as regards both their form 



