PLATE VII. 



Cidaris sceptrifera, Mantett, 1822. 



From the White Chalk.. 



Fig. 

 1 a. Test, dental organs, and spines, in situ, natural size. From the late Mr. Taylor's 

 collection, now in the Museum of the Royal School of Mines. P. 54. 



b. Dental apparatus and teeth, magnified two diameters. 



c. Ambulacral spine, greatly magnified. 



2. Spine of C. sceptrifera, variety. From the cabinet of the Rev. T. Wiltshire, F.G.S. 



Cidaris perorn a.ta, Forbes, 1850. 

 From the White Chalk. 



3 a. Lateral view of the test, natural size. In the British Museum. P. 62. 



b. Under surface of the same, natural size. 



c. Interambulacral plate, ambulacra, and poriferous zones, magnified three diameters. 



d. Lateral view of a primary tubercle, magnified. 



4 a. Inter-ambulacral spine, natural size. Museum of the Royal School of Mines. 



b. Stem, neck, head, and milled ring, magnified three diameters. 



c. A portion of the stem, magnified six diameters, to show the spiny ridges and the 



longitudinal lines in the valleys. 



