﻿22 FOSSIL ASTEROIDEA. 



Goniaster (Astrogonium) angustatus, Morris, 1854 Catalogue of British 



Fossils, 2nd ed., p. 80. 



Astrogonittm angustatum, Dujardin and Hupe, 1862. Hist. Nat. 



Zooph.Echin.(SuitesaBuffon), 

 p. 399. 



Goniaster (Astrogonium) angustatus, Forbes, 1878. In Dixon's Geology of 



Sussex (uew edition, Jones), 

 p. 368, pi. xxvi, fig. 10. 



Disk of medium size or relatively small and pentagonal. Rays elongate, 

 narrow, robust, and, though tapering, nearly uniform in breadth throughout. 

 Marginal contour stellate. Interbrachial arcs more or less flattened, which 

 emphasises the pentagonal outline of the disk. Margin thick and robust, much 

 highest in the region of the disk. Abactinal surface more or less convex, and was 

 probably somewhat inflated during life. Actinal intermediate plates very large, 

 covered with uniform granules. 



The supero-marginal plates are thick and massive, and they form a high and 

 broad border to the disk. There are only three supero-marginal plates between 

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

 each side of the disk. The fourth plate counting from the median interradial 

 line, and all the succeeding plates along the ray, 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. 



The supero-marginal plates which form the border of the disk are much larger 

 in the direction of height than any of the others. The plates on each side of the 

 median interradial line are about 4*75 mm. in breadth as seen on the abactinal sur- 

 face, and about the same measurement in length. They are convex abactinally, 

 and well rounded at the junction of the abactinal and lateral surfaces. Measured 

 in the margin their height is 8 mm., and their lateral surface (which forms the 

 vertical wall of the margin) is distinctly convex or pulvinate, but to a less degree 

 than their abactinal surface. 



The supero-marginal plates of the ray are not so high as those of the disk, 

 although their height is greater than their length. The height of the sixth plate 

 from the median interradial line is about 5 mm. Their abactinal and lateral sur- 

 faces form together a true segment of a circle, and this imparts a well-rounded 

 character to the ray. The plates are deeply bevelled at their junction with the 

 adjacent plates, and consequently distinctly pulvinate in the median line of breadth 

 and height. The surface of the plates is covered with minute punctations, but 



