BRITISH FOSSILS. 



3 



distorta, and constituting a conspicuous stratum in the middle division 

 of the Purbecks. A careful search, during which I was rewarded by 

 the discovery of several new forms of marine Purbeck mollusca, resulted 

 in the finding of a very perfect specimen of the body of the Hemici- 

 daris, now first described, accompanied by its spines, identical in struc- 

 ture with those previously observed. I have seen no traces of any other 

 Purbeck echinoderm. 



Explanation of the Plate. 



Fig. 1 . Body of the Hemicidaris Purbeckensis. 

 Fig. 2. Ambulacral and interambulacral plates. 

 Fig. 3. Base of a spine, natural size, 3 a, magnified. 3 b its section. 

 Figs. 4 and 4 a. Portions of the spines, natural size, indicating the dimensions and 

 proportions of those organs. 



JVote on the Species of Hemicidaris found in British Strata, 



At the time of the publication of Mr. Morris's " Catalogue of British Fossils " one spe- 

 cies only of Hemicidaris was known as British. Since then two others have been enume- 

 rated by Professor M'Coy, in his paper " On some New Mesozoic Eadiata," published in 

 the " Annals of Natural History" for December, 1848. 



I am acquainted with the following : — 



1. Hemicidaris intermedia, Fleming ; H. crenularis of British catalogues ; common in 

 the coralline oolite of Wiltshire ; rare in Dorsetshire. — {See Decade III., pi. 4.) 



2. Hemicidaris Purbeckensis, Forbes ; the new Purbeck species now first described 

 and figured. 



3. Hemicidaris alpina, Agassiz. (Echin. Suiss. ii., p. 52, tab. 18, figs. 19-22.) A pretty 

 species, easily distinguished from its congeners by the very small and thickly-set ambu- 

 lacral tubercles. Our attention has been called to it by Mr. S. P. Woodward. It was 

 found in the forest marble of Pickwick, Wilts, by Mr. Lowe of Chippenham. 



4. Hemicidaris pustulosa, Forbes. Avery fine new species from the great oolite of 

 Minchinhampton. It forms part of the collection of Mr. Lycett, and is figured in Plate A, 

 fig. 8, of the Monograph of Great Oolite Fossils to be published by the Palseontological 

 Society. Its nearest ally is the Hemicidaris diademata of Agassiz, which it resembles in 

 the sudden diminution and very small size of the uppermost interambulacral tubercles, 

 but differs in having the sutural granulated space of the interambulacral areas very wide. 



5. Hemicidaris icaunensis, Cotteau. (Echin. Foss. du Dep*. de I'Yonne, plate 3, 

 figs. 1-5.) ? I have provisionally identified with the species cited a great oolite urchin 

 from Minchinhampton, in Mr. Lycett's collection. It is figured in plate A, fig. 9, of the 

 Monograph of Great Oolite Fossils, published by the Palseontological Society. 



6. Hemicidaris confluens, M'Coy. In the Monograph already quoted a great oolite 

 Minchinhampton urchin is figured in plate A, fig. 10, which seems to agree with the 

 description of this species. 



7. Hemicidaris, Sp. Nov. ? In the collection of the Museum of Practical Geology. 

 Found in the cornbrash in a lane leading from Stourton Caundle to Lower Woodacre, 

 by Mr. Bristow, of the Geological Survey. This is a fine species, very distinct from 

 any other British one, resembling most nearly H intermedia, but differing in having 

 gradually (not suddenly) increasing ambulacral areas, with the tubercles upon them set 



