PLATE VIII. 



Cidaris Merceyi, Cotteau. 



From the White Chalk. 

 Fig. 



1 a. Under surface of the test, natural size. In the possession of Dr. Bowerbank, F.R.S. 



P. 60. 



b. Lateral view of the same, natural size. 



c. Inter-ambulacral plate, ambulacra, and poriferous zones, magnified three diameters. 

 (1. A lateral view of the same plate, magnified three diameters. 



e. A penultimate plate, from the upper part of one of the inter-ambulacral columns, 

 showing the small rudimentary tubercle and areolae, magnified three diameters. 

 /. A small inter-ambulacral plate, near the peristome, magnified three diameters, 

 y. A portion of an ambulacral area, and poriferous zones, magnified five diameters. 



2 a. Inter-ambulacral spine, natural size. 



h. A portion of the stem, magnified two and a half diameters. 



c. The head, neck, and part of the stem, magnified two and a half diameters. 



3. A small inter-ambulacral spine, natural size. 



Cidaris subvesiculosa, d'Orbipiy. 



From the White Chalk. 



4 a. Upper part of the test, and apical disc with one spine, in situ; natural size. From 

 the collection of Dr. Bowerbank, F.R.S. P. 57. 

 b. A plan of the apical disc, showing the parts that are absent in the preceding 

 figure. 



5. Lateral view of a smaller test. Dr. Bowerbank's collection. 



6, An ambulacral spine, highly magnified. 



