﻿NYMPHASTER OLIGOPLAX. 19 



All the supero- marginal plates are of uniform height, excepting the normal 

 diminution towards the extremity of the ray ; and all have the breadth greater 

 than the length. The plates on each side of the median interradial line measure 

 about 4 mm. in breadth and about 2 mm. in length ; and this length is maintained 

 with very slight diminution until about midway between the base and the extre- 

 mity of the ray, where the length is 1/75 mm., and the breadth is between 2'75 

 and 3 mm. Sixteen supero-marginal plates are preserved in the longest ray of 

 the specimen under description, counting from the median interradial line to the 

 broken extremity. A few plates are apparently missing. Measured in the 

 margin, the height of the plates is about 2*5 mm. 



All the supero-marginal plates are distinctly convex in the direction of their 

 median line of breadth, by which each plate is very clearly marked out, and a 

 highly ornate character is given to the species. The plates are also tumid and 

 well rounded on their marginal surface. The whole surface of the plates is 

 covered with rather large, widely spaced punctations or pits, which have a pecu- 

 liarly isolated appearance, unlike that of any other species (see PI. VIII, fig. 4 b). 

 I have not detected the presence of any pedicellariae upon this example. 



The remains of a few isolated plates are preserved on the abactinal area of the 

 fossil figured. They are all small and out of position, and are not available for 

 description. 



Dimensions. — The specimen figured on PI. VIII, fig. 4 a, has a minor radius of 

 about 12 mm. ; and the longest fragment of a ray preserved measures about 

 35 mm. The extremity is wanting. The thickness of the margin is 45 mm. The 

 breadth of the ray at the base between the third and fourth supero-marginal 

 plates counting from the median interradial line is from 8 to 8*5 mm. 



Locality and Stratigraphical Position. — The example described is from the 

 Upper Chalk near Bromley. It is preserved in the British Museum, and bears the 

 registration number 35,484. 



3. Nymphaster oligoplax, Sladen. PI. VIII, figs. 3a, 3b. 



Body of medium size. General form depressed and thin. Marginal contour 

 stellato-pentagonal. Rays narrow at the base and produced. Interbrachial arcs 

 wide and rounded. Margin thin. 



The supero-marginal plates form a broad border to the abactinal area of the 



