316 THE MEDALS OF CREATION. Cap. IX. 
of a less dense tissue than the outer coat, as is shown in the 
fractured spine in the figure. This structure does not exist 
in the spines of the depressed Turban Echinites, but is stated 
by M. Agassiz to prevail in all the species of the genus — 
Hemicidaris, of which the fossil figured in ZLign. 100 is 
the type. 
fiuttitee 
Alun 
Licn 101. CIDARITES FROM THE OOLITE AND CHALK. 
Fig. 1.—HEMICIDARIS INTERMEDIA; View in profile, showing the 
teeth projecting: 4 nat. Calne. 
2.—The same seen from above, displaying the outlet, and sur- 
rounding pores. 
3.—The same, view of the base, displaying the mouth, sur- 
rounded by five angular bipartite teeth. The ambulacral 
tubercles at the base are omitted in the figure. 
4—DIADEMA ROTULARE (Agass.); viewed in profile: nat. 
5.—A siliceous cast of another species of Diadema. South 
Downs. 
6.—View of the base of DIADEMA ROTULARE. This species 
occurs in the so-called Neocomian Formation of France. 
Crparis (Hemicidaris ?) wtermevia, Lign. 101, jig. i 
2, 3.—The shell of this echinite, from the Oolite at Calne, — 
so closely resembles that of H/. crenularis, above described, — 
