80 HEMICIDARIS. 



Locality and StratiffrapJiical position. — This species has been collected from the Great 

 Oolite of Minchinhampton. Many small specimens are found in the Oolitic shelly beds, 

 but they are not well preserved. One or two specimens in good preservation have been 

 found in a Clay seam of the same rock. In France it has been collected from the Bathonien 

 "Calcaire a polypiers," 11th Etage, d'Orhigny (Great Oolite of English authors), at Luc, 

 Langrune, Hanville, Calvados. 



History. — M. d'Orbigny, in 1847, separated this urchin from Hemicidaris crenularis, 

 with which, he says, he was confounded by M. Agassiz. He further observes, it is easily 

 distinguished from Hetnicidaris crenularis by a much greater number of small tubercles 

 between the large inter-ambulacral tubercles ; but this is clearly a mistake, for both spe- 

 cies have two rows of close-set granules down the centro-sutural line. The difference 

 resides more in the structure of the ambulacra, and in the size and prominence of the 

 apical disc, than in the number and arrangement of the inter-ambulacral granules. It is 

 now figured and described for the first time. 



Hemicidaris mince, Agassiz. PI. Ill, fig. 5 a, b, c, d. 



Hemicidaris minor. Agassiz, Catalogus Systematicus, p. 9. 



— — Agassiz and Desor, Catalogue raisonne des Echinides, Annales 



des Sciences Naturelles, torn, vi, p. 339, 3d series. 

 AcROSALENiA RARiSPiNA. M'Coy, Annals of Natural History, 2d series, vol. ii, p. 411, 

 Hemicidaris minor. Wright, Annals of Natural Histor}^ 2d series, vol. xiii, pi. 2, 



fig. 3 a — c, p. 165. 



— — Desor, Synopsis des Echinides Fossiles, p. 56. 



— — Morris, Catalogue Brit. Foss. 2d edit., additional species of Echi- 



nodermata. 



Test hemispherical above, flat at the base; ambulacral areas slightly flexuous, not 

 prominent, with six large semi-tubercles at the base, and four rows of small, unequal- 

 sized granules in the middle, diminishing to two rows in the upper part of the areas ; 

 inter-ambulacral areas three times the width of the ambulacral, with three primary tuber- 

 cles on the upper surface, and three smaller ones at the base ; the wide miliary 

 zones are covered with small, distinct, nearly equal-sized miliary granules, which form 

 complete circles around the margins of the areolas of the primary tubercles ; the apical 

 disc is of moderate size, and its ovarial plates are covered with a delicate granulation ; 

 base flat, mouth opening large, peristome unequally decagonal, pores arranged in the zones 

 in single pairs throughout. 



Dimensions. — Height, three tenths of an inch ; transverse diameter, nine twentieths 

 of an inch. 



