FROM THE INFERIOR OOLITE. 73 



History. — This species was first figured in my ' Memoirs on the Cidaridae of the 

 Oolites,' published in the 'Annals of Natural History,' October, 1851. It is a very rare 

 Urchin ; fine specimens of it are contained in the British Museum, Bristol Museum, and 

 in my collection ; the only known localities are those already mentioned. 



Hemicidaris pustulosa, Agassiz. PI. Ill, fig. 1 a, b, c, d, e. 



Hemicidaris pustulosa. Agassiz, Catalogus Systematicus, p. 8. 



— — Agassiz and Desor, Catalogue raisonne Annales des Sciences 



Naturelles, 3 e serie Zool. tome vi, p. 338- 



— — Desor, Synopsis des Echinides Fossiles, p. 53. 



— — D'Orbigny, Prodrome de Pale'ontologie, tome i, p. 320, No. 420. 



Test large and sub-conoidal ; ambulacral areas wide and straight ; semi-tubercles large, 

 wide asunder, upper part covered with homogeneous granules, those on the margins the 

 largest ; inter-ambulacral areas narrow, with two rows of prominent primary tubercles, 

 which disappear a little way above the equator ; the uppermost four or five tubercular 

 plates have clusters of from six to ten homogeneous granules developed on their surface ; 

 apical disc large and very prominent, the elements thereof forming a considerable elevation 

 on the test ; mouth opening large. Spines thick, oval, with a ridge on one side. 



Dimensions. — a. Agassiz's type specimen, from the Great Oolite, Ranville. Height, 

 one inch and one twentieth of an inch ; transverse diameter, one 

 inch and seven tenths of an inch. 

 b. Height of the specimen figured (PI. Ill, fig. 1), seven tenths of an 

 inch ; transverse diameter, one inch and three tenths of an inch. 



Description. — In the examination of the species of the genus Hemicidaris, the palaeon- 

 tologist often experiences much difficulty in finding on the test alone good characters for 

 the separation of forms which, from the study of the entire organism, he knows to be dis- 

 tinct, but which, were he to rely merely upon the shell, he would pronounce to be identical ; 

 this circumstance has doubtless led to much confusion among the members of this group ; 

 no such difficulty, however, exists in the species now under consideration, as it is marked 

 by characters so prominent and well defined, that when it is once seen it cannot possibly 

 be mistaken for any but one of its congeners. 



Hemicidaris pustulosa was first discovered by Professor Peslongchamps, in the Great 

 Oolite of Normandy, and entered by Agassiz in his ' Catalogus Systematicus. These 

 specimens have been most kindly communicated to me by Professor Deslongchamps. 

 But it has never, until now, been either figured or described. 



The test is large, with a broad base ; it is inflated about the equator ; from this point 



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