14 FOSSIL ASTEROIDEA. 



type of a distinct species. More material is needed before such a step would be 

 warranted. 



Dimensions. — The large example figured on PI. II, fig. 1 a, has a major radial 

 measurement of from 80 to 95 mm. or more, with a minor radius of about 52 mm. 

 The breadth of the ray between the sixth and seventh infero-marginal plates, 

 counting from the median interradial line, is about 17 or 18 mm. 



Locality and Stratigrapliical Position. — This species appears to be confined to 

 the Lower Chalk. Examples have been collected from Washington, Amberley, 

 Southerham, and Glynde, in Sussex. Also from the Lower Chalk of Folkestone, 

 and the Chalk Marl of Dover. 



History. — Two examples of this species were first figured by Forbes in Dixon's 

 ' Geology and Fossils of the Tertiary and Cretaceous Formations of Sussex,' 

 London, 1850, pi. xxiii, figs. 4 and 5. Both these specimens are now preserved 

 in the British Museum. One example, which is from Amberley, is drawn on 

 PI. Ill, fig. 1 a. The other, which is from Washington, is accurately represented 

 by fig. 3 a of the same plate. 



Variations. — In addition to the difference noted above in the form of the 

 stellate bases of the abactinal plates or paxillse, other minor differences may be 

 observed. In some examples the breadth of the border formed by the marginal 

 plates on the disk area is not relatively so great as in other examples, and the 

 proportions of length to breadth, as well as the amount of tumidity of the 

 component plates, are subject to variation. In some examples, again, the irregu- 

 lai'ity in the granulation of the marginal plates, arising from the former presence 

 of coarser granules interspersed amongst the average granulation, is more marked 

 than in others. These differences will be more readily noticed by turning to the 

 figures given on PI. II and PL III than by a lengthy verbal description. Some of 

 tlie examples come from difi'erent beds and different localities — circvimstances 

 which I consider to be sufficient to account for the variation. 



G^emis— NYMPHASTER, SJaden, 1885. 



Nympuaster, Sladen. In Narr. Chall. Exp., 1885, vol. i, p. 612 ; Zool. Chall. 



Exped., part li, Eeport on the Asteroidea, 1889, p. 294. 



Disk large and flat. Rays elongate, slender, tapering, and almost square in 

 section. Marginal plates forming a broad border to the disk, and either united 



