26 FOSSIL ASTEROIDEA. 



of alternating granuliform eminences and depressions, upon which the spinelets 

 constituting the armature of the adambulacral plates were originally borne. 



The actinal interradial areas are small, and are covered with regular pentagonal 

 or rhomboid intermediate plates, which are arranged in series parallel to the 

 ambulacral furrow, and form a compact, mosaic-like pavement. The actinal inter- 

 mediate plates are moderately large in relation to the size of the disk. The plates 

 of the series adjacent to the adambulacral plates are sensibly larger than any of the 

 others, and the plates of the next series are also larger than those which form the 

 rest of the pavement. Near the infero-marginal plates the actinal intermediate 

 plates become small and more or less irregular. The intermediate plates extend 

 at the base of the ray to about the fifth infero-marginal plate, counting from the 

 median interradial line. The surface of the plates is covered with rather large, 

 widely spaced, and deeply sunken punctations, upon which granules were pre- 

 viously borne, and these would appear to have been comparatively large in size and 

 uniform (see PI. IV, fig. 1 b). 



From what is visible of the margin of this example it is seen that the supero- 

 marginal series of plates are nearly of the same height as the infero-marginal 

 series, and are similar in structure. 



Unfortunately no other portions of this fragment are available for description. 



Localitjj and Stratigraphical Position. — The specimen upon which this species 

 was founded was collected by Mr. Samuel Woodward, from the Upper White 

 Chalk, near Norwich. 



Dimensions. — In the type specimen (figured on PI. IV, fig. 1 a) the major 

 radius is about 35 mm., and the minor radius about 18 mm. Breadth of the ray 

 between the fifth and sixth infero-marginal plates about 10 mm. 



History. — The type specimen was figured by Woodward in his ' Outline of the 

 Geology of Norfolk,' pi. v, fig. 1, and is now preserved in the collection of the 

 Norfolk and Norwich Museum. It was kindly lent by the committee of that 

 institution to Dr. Wright for the purpose of this monograph. It has been 

 carefully drawn on PI. IV, figs. 1 a — 1 c. An admirably executed cast of this 

 specimen is in the British Museum. I am not at present aware of the existence 

 of any other examples of this rare form. 



Remarks. — The example referred by Forbes to this species, and figured by 

 him in Dixon's ' Geology and Fossils of the Tertiary and Cretaceous Formations 

 of Sussex,' London, 1850, pi. xxiii, fig. 9, belongs to a distinct species, which I 

 have named Peidagonaster megaloplax. A number of other specimens in other 



