MITRASTER HUNTERI. 59 



1. MiTEASTER HuNTEEi, Forbes, sp. PI. IX, figs. 3 ft— 3 e -, PI. XII, figs. 3 a — 3 e ; 



PI. XV, figs. 3 a— 5 b. 



GoNiASTEU EEOULABis, Mantell, 1844. Medals of Creation, vol. i, 



p. 335, lign. 73 (non Linck). 



GoNiASTEE (GoNiODiscus) HuNXKBi, Forbes, 1848. Memoirs of the Geological 



Survey of Great Britain, vol. ii, 

 p. 471. 



— — — Forbes, 1850. In Dixon's Geology and 



Fossils of the Tertiary and Creta- 

 ceous Formations of Sussex, 

 London, 4to, p. 331, pi. xzi, fig. 1. 



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



2nd ed., p. 81. 

 AsTHOGONiUM HuNTEEi, Dujardtn and Hupi, 1862. Hist. Nat. 



Zooph. Echin. (Suites a Buffon), 



p. 399. 

 GoNiASTEK (GoNiODiscus) HuNTEEi, Forbes, 1878. In Dixon's Geology of Sussex 



(new edition, Jones), p. 365, 



pi. xxiv, fig. 1. 



Body of small size. General form depressed. Abactinal surface flat and 

 apparently depressed within the boundary of the supero-marginal plates, the 

 gibbosity of the latter and their centrally sloping surface giving a concave character 

 to the area generally in fossil examples, which was probably always more or less 

 present. Actinal surface flat or with a tendency to be sliglitly convex. Marginal 

 contour subcircularly pentagonoid, the sides being sliglitly convex or bulging out- 

 ward. The major radius is proportional to the minor radius as 100 : 90"47 approxi- 

 mately ; and the rays are not produced, the angles of the pentagon being obtusely 

 rounded. Margin thick and well rounded, the slope being more gradual on the 

 actinal surface. 



The supero-marginal plates are three in number counting from the median 

 interradial line to the extremity, or six from the tip of one ray to the tip of the 

 adjacent ray, exclusive of the odd terminal or " ocular " plate in each case. They 

 form a broad border to the abactinal area of the disk, of uniform breadth through- 

 out, which measures about 6*3 mm. at the median inten-adial line in an example 

 whose diameter (R -\- r) measures about 40 mm. Excepting the ultimate plates 

 all the supero-marginal plates are of equal size and uniform, tlio breadth being 

 a little more than once and a half the length, the actual measurements in the 



