﻿PYCNASTER ANGUSTATUS. 23 



these are so extremely faint that they are seen with difficulty. They are probably 

 weather-worn in the example under notice. 



The infero-marginal plates, as seen in the direct lateral view of the margin, are 

 much smaller in height than the supero-marginal series in the type specimen. 

 The plates which form the margin of the disk are higher than long, the height 

 being about 5 mm. and the length about 3 - 25 mm. in those adjacent to the 

 median interradial line ; the succeeding plates on the margin of the disk are each 

 less in height than the preceding plate, the third or fourth plate, counting from 

 the median interradial line, having the height and length about equal. The infero- 

 marginal plates along the ray have the length greater than the height. The 

 surface of the infero-marginal plates resembles that of the superior series in the 

 character of its punctation. 



Traces of small excavate pedicellarias are present on occasional plates, but 

 these appear to have been very few in the example under description. 



On the abactinal surface of the disk a few isolated and displaced plates are 

 present. Some of these seem rather thick and tuberculous in character, but the 

 state of the preservation of this part of the fossil is unfortunately quite unfitted 

 for description. 



There is a fine fragment of this species preserved in the Museum of Practical 

 Geology, Jermyn Street, from the Upper Chalk of Bromley, which shows part of 

 the actinal surface. The infero-marginal plates in the disk are very high in this 

 example, and five of them in an interbrachial arc bear a small foraminate pedi- 

 cellaria. This is situated near the upper margin of the plate, about equidistant 

 from that margin and the lateral margins of the plate, and consists of a small 

 round foramen situated in the middle of a very shallow concavity, and with five 

 or six faint channels radiating from the foramen to the margin of the concavity, 

 gradually thinning and dying out there. The channels radiate like the spokes of 

 a wheel, or a five-rayed star, and produce a facies unlike that of any other pedi- 

 cellarian apparatus with which I am acquainted. The actinal intermediate plates 

 are very large, and not more than three series are present. The plates of the 

 series next to the adambulacral plates are much larger than the others, and are 

 broader than long. The adambulacral plates are broader than long, and their 

 surface is marked with three or four ridges parallel to the furrow, upon which 

 spinelets were previously borne. The furrow series consists of about five 

 spinelets. A few of these spinelets are preserved, and they are rather short, 

 cylindrical, and slightly tapering. The mouth-plates are very small and narrow. 



Dimensions. — The specimen figured on PL IX, fig. 1 a, has a minor radius of 

 about 23 mm. The longest portion of a major radius preserved is 53 mm. ; the 

 ray is broken abruptly, and there is very slight diminution in the breadth at the 



