FROM THE INFERIOR OOLITE. 71 



Section a. — Test elevated, tubercles large in the upper parts of the inter-ambulacra. 



Examples : Hemicidaris intermedia, Ilemicidaris cremdaris, Ilemi- 



cidaris Bravenderi. 

 Section b. — Test large, depressed ; tubercles suddenly diminishing in size on the upper 



part of the inter-ambulacra. 



Examples : Hemicidaris diademata, Ilemicidaris Stokesii, Hemicidaris 



pustulosa. 

 Section c. — Test in general small ; ambulacra very flexuous ; tubercles in the inter- 

 ambulacra few in number, but large in size, and very prominent. 



Examples : Hemicidaris minor, Hemicidaris Thurmanni. 



A. Species from the Inferior Oolite. = 10M Mage, Bajocien, d'Orbigny. 

 Hemicidaris granulosa, Wright. PI. Ill, fig. 2 a—f 



Hemicidaris granulosa. Wright, Annals and Magazine of Natural History, 2d series, 



vol. viii, p. 257, pi. ii, fig. 4 a, a. 



— Desor, Synopsis des Echinides Fossiles, p. 55. 



— — Morris, Catalogue of British Fossils, 2d edit., p. 82. 



Test sub-spheroidal, depressed at both poles ; ambulacral areas straight, with two mar- 

 ginal rows of prominent, well-defined, imperforate granules, and three pairs of semi-tubercles 

 at the bases thereof; inter-ambulacral areas, with three pairs of primary tubercles, extending 

 only as far as the equator, the upper tubercular plates being covered with warty granules ; 

 apical disc large, and not prominent ; base flat ; mouth opening large ; peristome slightly 

 notched. 



Dimensions. — Height, seven tenths of an inch ; transverse diameter, one inch and one 

 tenth. 



Description. — This remarkable Urchin is closely allied to Hemicidaris pustulosa, Agassiz, 

 and replaces that Dorsetshire species in the same zone of the Inferior Oolite at Dundry- 

 The test is hemispherical, flat below, and slightly depressed above (PI. Ill, fig. 2 c) ; the 

 ambulacral areas are straight and prominent, they have two marginal rows of from ten to 

 twelve large, prominent, imperforate granules, which are smooth and deformed, and set 

 regularly in alternate rows, the intervening surface of the plates being filled with small, 

 ill-defined, and irregularly arranged miliary granules (PI. Ill, fig. 2 d) ; the bases of the 

 areas are wide, to allow of the development of three pairs of moderately sized semi-tubercles 

 (PI. Ill, fig. 2 b) ; the poriferous zones are nearly straight, except where they follow the 



