114 PSEUDODIADEMA. 



the apical disc is always broken, but the spines are sometimes adherent to the test (fig. 2i). 

 It has been collected by M. d'Orbigny in the Inferior Oolite of Saint Honorine, Ranville, 

 where it is abundant. I have before me a specimen collected from the " Oolite Ferru- 

 gineuse de Bayeux " so closely resembling some of those from Cricldey Hill, that it might 

 readily be taken for an urchin from that locality. My friend M. Deslongchamps, who has 

 kindly lent me this specimen for comparison, observes, " seul exemplaire que j'ai trouve ;" 

 so that it must be rare in Normandy. It has been obtained by M. Cotteau from the 

 Ferruginous Oolite, of " Tour-du-Pre, pres Avallon, departement de I'Yonne," which bed 

 lies upon the Calcaire a Entroques, the true equivalent of the Dundry, Cotteswold, and 

 Dorsetshire beds of the Inferior Oolite. 



History. — Pseudodiadema depressum was first mentioned in the ' Catalogue raisonne 

 des Echinides' by Agassiz and Desor, but was neither figured nor described by 

 them. This, however, has been done by M. Cotteau, in his ' Etudes sur les Echinides 

 Eossiles.' In both countries it appears to characterise beds belonging to the same 

 geological horizon. 



C. Species from the Stonesfield Slate. 

 Pseudodiadema Parkinsoni, Desor. PL VI, fig. 4. 



Pseudodiadema Pabkinsoni. Desor, Synopsis des Echinides Fossiles, p. QQ. 



Parkinson's Organic Remains, vol. iii, pi. 1, fig. 8, not named 

 in this work. 



Test small, circular, depressed ; ambulacral areas wide ; tubercles of the inter-ambu- 

 lacral areas a little larger than those of the ambulacral ; no secondary tubercles ; spines 

 thick, subulate, and a little bent, nearly as long as the diameter of the test, surface covered 

 with longitudinal lines. 



Dimensions. — Transverse diameter, three fifths of an inch ; height unknown. 



Description. — This pretty little Diadem has been overlooked by all English authors 

 except Parkinson, who figured it in his ' Organic Remains,^ and only observes (vol. iii, 

 p. 10), "This very uncommonly perfect specimen from Stunsfield, Oxfordshire (PL I, 

 fig. 8), in which a considerable number of spines are still adherent to the shell, appears to 

 be of the same species with the last fossil " (a Wiltshire Pseudodiadema). M. Desor, in 

 his ' Synopsis,' names this species ParJcinsoni, and adds the following note : " Je ne connais 

 cette espece que par la jolie figure qu'en a donnee Parkinson. II est surprenant qu'aucun 

 des auteurs Anglais ne I'ait encore mentionnee, ni ne lui donne un noni. Parkinson s'est 

 borne a, la fignrer sans lui imposer un nom." 



