58 DIPLOCIDARIS. 



and Inferior Oolite of Somersetshire has not yet been accurately defined ; and indeed it 

 is only by palaeontological characters that the one rock can be distinguished from the 

 other. Lithologically, the rock in which Dij)locidaris Desori is imbedded reminds me more 

 of the Upper Lias of that region than of the Inferior Oolite. 



I dedicate this species to my friend M. Desor, who has established the genus to 

 which this urchin is referred. 



B. Species from the Inferior Oolite. 

 DiPLOCiDARis Wrightii, Besor. PI. I, fig. 5 a, h. 



\_Species of which the test is unknown.'] 

 DiPLOciDAKis Wrightii. Desor, Synopsis des Echinides Fossiles, p. 45, pi. 7, fig. 24. 



The spine on which M. Desor estabhshed this species was figured in my ' Memoir on 

 the Cidaridse of the Oolites/ and was, by mistake, drawn with the spines since ascertained 

 to belong to Cidaris Fowleri. The articulating head is small, the rim of the acetabulum 

 deeply crenulated, and the cup largely perforated ; the ring is carinated and finely 

 milled ; one half of the neck is covered with longitudinal lines, and the other half is 

 smooth (PI. I, fig. 5 b) ; the stem is round, and gradually swells out towards the middle, 

 where it is fractured ; it is covered with small pustules, which are rather irregularly dis- 

 posed on the surface, and not arranged in lines. M. Desor says it resembles the spines 

 of Diplocidaris gigantea, but the stem is more swollen out in the middle than in that 

 Corallian species. 



Locality and StratigrapJncal position. — I have fragments of three spines, which 

 Avere all collected in the Pea Grit, Inferior OoUte, at Crickley Hill, along with the test and 

 spines of Cidaris Fowleri. 



