FROM THE CORALLINE OOLITE. 93 



fine longitudinal lines ; base tumid, with a prominent milled ring below, and a second 

 smooth ring above. Jaws large and powerful. 



Dimensions. — 1 c. Height, one inch and one tenth of an inch ; transverse diameter, 

 one inch and three fifths of an inch. 

 1 i. Height, one inch and three fifths of an inch ; transverse diameter, 

 one inch and three fifths of an inch. 



Description. — This is one of the most common, and, at the same time, one of the most 

 beautiful and typical examples of the genus Hemicidaris in our English rocks. Like its 

 associate, Cidaris florigemma, it has long been mistaken for a foreign species {Hemi- 

 cidaris crenularis) which has not yet been found in our Coralline Oolites. 



Had the determination of this species rested on the anatomy of the shell alone, it 

 would have been almost impossible to distinguish between these two species; but, 

 fortunately, M. Agassiz has given a fine figure and detailed description* of Hemicidaris 

 crenidaris of Switzerland, said to be the type of Lamarck's species. This magnificent 

 specimen, with its spines attached, was found in the Corallien etage of Besan^on, and 

 formed part of the collection of M. le Comte Dudressier, which Herr Suess informs me 

 is in the Imperial Museum of Vienna. Now as Lamarck's Cidaris crenularis came from 

 Switzerland (" Habite, Fossile de la Suisse"!), we cannot doubt the identity of the specimen 

 figured by Agassiz with the Lamarckian type. These points having been settled, it is easy 

 to show that this English Hemicidaris is very distinct from the Swiss one, for although the 

 tests can only critically be distinguished from each other, still the spines of the Swiss 

 urchin are so very difierent from the EngHsh form, that there cannot be a doubt about the 

 distinctness of the species. In Hemicidaris crenularis the spines form large clubs, which 

 gradually increase in diameter from the head to the extremity, whereas in Hemicidaris 

 intermedia they gradually taper from the head to the point. 



The first good figure of Hemicidaris intermedia was given by Parkinson in his 

 ' Organic Remains,' and described as a mammillated Echinite from Wiltshire, which 

 " should perhaps be considered a variation of Cidaris papillata." X Mantell gave a reduced 

 copy of Agassiz's figure in his ' Medals of Creation,' vol. i, p. 340, observing, however, — 

 " This species {Hemicidaris crenularis) of mammillated Echinus is common in the Oolite of 

 this country, and is considered to be characteristic of the Upper Jura limestone; it is said 

 to be the same as that figured by Mr. Parkinson, under the name of Cidaris mummillafa, 

 from Calne, in Wiltshire ; but I have never observed spines like those of Agassiz's figure 

 in the English Oolite. These spines are not homogeneous throughout, but their central 

 part appears to have been of a softer texture than the external crust, as may be seen in the 



* ' Echinodermes Fossiles de la Suisse,' seconde partie, pi. 18, figs. 23 and 24, p. 44. 

 f ' Histoire Naturelle des Animaux sans Vertebres,' 2d e Jit. tome iii, p. 384, 

 X Parkinson, 'Organic Remains,' vol. iii, p. 14. 



