﻿6 FOSSIL ASTEROIDEA. 



Another point of difference is to be found in some of the fossil forms which are 

 referred in the following pages to the genus Galliderma ; and this consists in the 

 separation of the supero-marginal plates, at least at the base of the ray, by one or 

 more series of medio-radial plates. It is a character whose importance is not to be 

 under-estimated, but too little as yet is known of the morphological plasticity of 

 the genus to justify in my opinion the separation of the forms on this ground 

 alone. I prefer, therefore, to regard this extension of the abactinal plating as a 

 transitional character, and I believe that this opinion is warranted by the range of 

 plasticity observed in other genera of recent Asteroidea. 



1. Callideema Smiths, Forbes, sp. PI. I, figs. 1 a — If; PI. VIII, figs, 2 a — 2 c. 



Goniasteb (Astbogonium) Smithii, Forbes, 1848. Memoirs of the Geological 



Survey of Great Britain, vol. ii, 

 p. 474. 



— — — — 1850. In Dixon's Geology and 



Fossils of tbe Tertiary and Cre- 

 taceous Formations of Sussex, 

 London, 4to., p. 334, pi. xxii, 

 figs. 1 and 2. 



— — Smithii, Morris, 1854. Catalogue of British Fossils, 



2nd ed., p. 80. 

 Astbogonium Smithii, Dujardin and Hupe, 1862. Hist. Nat. Zooph. 



Echin. (Suites a Buffon), p. 399. 

 Goniasteb Smithi, Quenstedt, 1876. Petref'actenkunde Deutsch- 



lands, I. Abthl., Bd. iv, p. 64. 



— (Asteogonium) Smithije, Forbes, 1878. In Dixon's Geology of Sussex 



(new edition, Jones), p. 367, 

 pi. xxv, figs. 1, 2, 2 a. 



Body of large size. General form depressed. Abactinal area probably capable 

 of slight inflation, and more or less flexible : a slight carination being present in 

 the radial abactinal regions. Actinal surface flat. Marginal contour stellato- 

 pentagonal, the major radius measuring rather more than twice the minor radius. 

 Rays broad at the base and tapering gradually to the extremity. Interbrachial 

 arcs well rounded and forming a regular curve. Margin thick, with a well-defined 

 channel traversing the line of junction of the supero-marginal and infero-marginal 

 series of plates, formed by the tumid character of the marginal surface of both 

 series of plates. 



The infero-marginal plates are about twenty or twenty-one in number, counting 



