﻿NYMPHASTER COOMBII. 17 



Lower Chalk of Glynde, Sussex ; as well as from the Lower Chalk of Dover and 

 the Isle of Wight. Other specimens of Nymphaster, as to the reference of which 

 to N. Coombii I am more or less doubtful, which show certain differences in 

 structural details, are from the Grey Chalk of Folkestone and Dover, and from 

 the Lower Chalk of Betchworth. Several examples in the Museum of Practical 

 Geology, Jermyn Street, are labelled from the " Upper Chalk," but I am inclined 

 to think that their reference to that horizon is more or less doubtful. 



History. — The type of this species was found by Mr. G. Coombe at Balcombe 

 Pit, Amberley, and formed part of Mr. Dixon's collection. It is now preserved in 

 the British Museum. It was first figured by Edward Forbes in Dixon's "' Geology 

 and Fossils of the Tertiary and Cretaceous Formations of Sussex,' London, 1850, 

 pi. xxiii, fig. 6. The same specimen is carefully represented on PI. VIII, figs. 1 a, 

 1 b of this memoir. 



Doubtful Examples of this Species. — Three specimens are figured on PL VII, 

 which I only place provisionally and with very great doubt under this species. I 

 do not, therefore, at present propose to describe them in detail, or to definitely 

 assign the characters they present as supplementary to those already given as 

 belonging to Nymphaster Coombii. 



1. An example from the Lower Chalk of Betchworth, in which a portion of the 

 actinal surface is preserved (PI. VII, figs. 1 a — 1 e). This specimen shows large 

 infero- marginal plates somewhat longer in proportion to their breadth than in the 

 type specimen, and their surface is covered with an extremely fine uniform puncta- 

 tion. The latter character is altogether unlike that of examples which I consider 

 to be true forms of Nymphaster Coombii. But from this character alone, which 

 recent forms show to be one subject to considerable variation, I shrink from 

 taking any more definite step, at least until further material is available for study. 

 This example has some of the adambulacral plates and actinal intermediate plates 

 well preserved. The adambulacral plates (see PI. VII, fig. 1 c) conform to the 

 description given above. The actinal intermediate plates are rhomboid in form, 

 and their surface is covered with deep, large, well-spaced pits, which indicate the 

 former presence of a coarse uniform granulation. These plates are shown on 

 PI. VII, fig. 1 e. The margin of this example is quite characteristic of Nym- 

 phaster Coombii. The infero-marginal plates are seen to be low and more or less 

 bevelled or sloping towards the margin ; whilst the supero-marginal plates are 

 relatively rather higher and more abruptly bent at the junction of the actinal and 

 lateral surfaces (see PI. VII, fig. 1 b). 



2. This is a badly preserved specimen from the Grey Chalk of Folkestone, in 

 which nothing but the supero-marginal plates and the general outline are available 



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