PLATE V. 



Cidaris clavigera, Konig, 1822. 



From the White Chalk. 



Fig. 

 1. Test, with dental organs and spines, natural size. From Mr. Taylor's collection, 

 now in the British Museum. P. 48. 



2 a. Lateral view of a fine test, natural size. British Museum. 

 b. The under surface of the same, natural size. 



3. The apical disc, showing the ovarial, ocular, anal plates, and madreporiform body, 



magnified two and a half diameters. British Museum. 



4. A portion of the peristomal membrane and oral plates, with part of the dental 



organs, magnified two and a half diameters. British Museum. 



5 a. An abnormal inter-ambulacral spine, natural size. British Museum. 

 b. The same, magnified, to show the position and form of the canals passing through 

 ,the stem. 



6. An abnormal spine, with summit excavated, natural size. This specimen belongs 

 to the Rev. T. Wiltshire. 



7 — 14. Varieties of large inter-ambulacral spines, belonging to the British Museum, 

 natural size. British Museum. 



15. A remarkable abnormal form, with an enlarged neck and conical stem and apex, 

 natural size. British Museum. 



Cidaris sceptrifera, Mantell, 1822. 



From the White Chalk. 



16. Upper surface of a fine test, natural size, with the apical disc in situ. This 

 specimen belongs to Dr. Bowerbank's collection. P. 54. 



17 a. Under surface of the same, natural size. 

 b. Lateral view of the same. 



