PLATE II. 



. Cidaris from the Upper Greensand and Grey Chalk. 

 Cidaris Bowerbankii, Forbes, 1850. 



From the Grey Chalk. 



Fig. 



1 «. Test and spines, in situ, natural size, belonging to Dr. Bowerbank, F.R.S. P. 45. 



b. Au inter-ambulacral spine, magnified three times. 



c. The head, milled ring, and neck, highly magnified. 



d. A small ambulacral spine, highly magnified. 



Cidaris velifera, Bronn, 1857. 

 From the Upper Greensand. 



2 a. A lateral view of the test, natural size, in the collection of W. Cunnington, Esq., F.G.S. P. 37. 



b. Basal portion of the same, magnified twice. 



c. Dorsal portion of the same, magnified twice. 



d. Lateral view of the same, magnified twice. 



e. Inter-ambulacral plate, a portion of the ambulacra and poriferous zones, magnified five times. 

 /. A lateral view of a primary tubercle with its circle of areolar granules, magnified. 



3 a. One of the inter-ambulacral spines, natural size. 

 b. The same spine, magnified twice. 



4 a. Cidaris velifera, a portion of the test and spines, in situ, natural size. This unique specimen is 



in the cabinet of Mr. W. Cunnington. 

 b. The head of a spine, with its milled ring, highly magnified. 



Cidaris vesiculosa, Goldfuss, 1826. 

 From the Upper Greensand and Grey Chalk. 



5 a. Upper surface of the test, natural size. This specimen from the Upper Greensand is in the possession 



of W. Cunnington, Esq., F.G.S. P. 41. 



b. Basal portion of the same test, natural size. 



c. Lateral view of the same test, natural size. 



d. An inter-ambulacral plate, witb ambulacra and poriferous zones, magnified three times. 



Cidaris Farringdonensis, Wright, 1864. 

 From the Lower Greensand. 



6, 7. Single iuter-ambulacral plates from the Sponge-Gravel, near Farringdon, magnified two diameters. 



Museum of Royal School of Mines. 

 Sa.b,c. Different inter-ambulacral spines of this species. Museum of Royal School of Mines. 

 c, a. Basal portion of one magnified three times. 



