PLATE I. 



Cidaris from the Gaulf and Grey Chalk. 



CiDAKis Carteri, Forbes, 1854. 



From the Grey Chalk. 

 Fig. 



1 a. Upper surface, showing the disc, natural size. From the collection of James Carter, 



Esq. P. 39. 



h. Lateral view of the same, shomng the height of the test and the prominence of the 

 discal elements. 



c. A single inter-ambulacral plate, with a portion of the ambulacra! area and poriferous 



zones, magnified. 



d. Apical disc, with the ovarial and ocular plates, magnified. 



e. Portion of a spine, magnified. 



f. A small ambulacral spine, magnified. 



Cidaris Gaultina, Forbes, 1854. 

 From the Gault. 



2 a. Test and spines, i» situ. British Museum. P. 36. 



b. Inter-ambulacral plate, magnified two and a half times. 



c. One large primary spine, natural size. 



d. A portion of ditto, near the base, magnified twice. 



e. Stellate terminal portion of a primary spine, magnified. 



3 a. A primary spine, natural size. 

 b. The same, magnified twice. 



4 «. A primary spine, with expanded stem. 



b. The same, magnified twice. 



c. A view of the tenninal portion. 



