272 Dr. T. Wright on the Cidaridas of the Oolites. 



centre of the areas two rows of secondary tubercles are arranged 

 which separate the principal ranges from each other, and like 

 rows of secondary tubercles separate the principal tubercles 

 from the ambulacral areas. These secondary tubercles are very 

 irregular as to size and arrangement, and are in general best 

 developed at the base and equator of the test ; besides the pri- 

 mary and secondary tubercles, the surface is studded with small 

 granulations. The mouth-opening is large and decagonal, and 

 its margin is divided by deep notches. The lobes which cor- 

 respond to the ambulacral areas are twice as large as those 

 corresponding to the interambulacral areas. The apical disc is 

 broken in the specimen before me. According to Agassiz the 

 oviductal apparatus is generally very apparent. The ovarial 

 plates are large and pentagonal ; their summit forms a pro- 

 minent angle which advances into the interambulacral areas. The 

 madreporiform plate is larger than the pairs of plates, and like 

 them is perforated and finely granulated. The ocular plates are 

 very small and inserted between the angles of the ovarials and 

 dovetailed with the apex of the ambulacra. The anal opening is 

 large and of a circular form. The spines are long, needle- 

 shaped, and finely striated longitudinally. 



Affinities and differences. — The size of this species, the arrange- 

 ment of the secondary tubercles, and the structure of the pori- 

 ferous avenues form a group of characters by which it is readily 

 distinguished from its congeners. 



Locality and stratigraphical range. — The specimen before me 

 was obtained from the Coral Rag of Wiltshire or Oxfordshire ; 

 it is found in the Corallian stage of Besancon, canton of Soleure, 

 in Switzerland, and in the Coral Rag of Angoulin, near Rochelle, 

 in France. 



History. — Figured and accurately described for the first time 

 by M, Agassiz in his f Echin. Foss./ and now first figured and 

 registered as a British fossil. 



Genus Pedina, Agassiz. 



Test thin, circular and depressed ; primary tubercles very 

 small, but still perforated and crenulated like those of Diadema. 

 Pores arranged in triple oblique pairs as in the genus Echinus. 

 Mouth small, slightly decagonal; margin not much notched. 

 The ovarial disc not prominent ; the surface of the test com- 

 paratively smooth when compared with the other genera of the 

 Echinidce. The ambulacral areas have two ranges of tubercles, 

 and the interambulacral areas have two ranges of primary, and 

 one or more rows, more or less complete, of secondary tubercles, 

 situated at the external and internal sides of the primaries. This 



