PLA.TE XX. 



From the Lower Greemnnd. 



Fig. 1 a. PsEUDODiADEMA IMai.bosi, Af/assiz. Upper surface of the test, natural size. 

 From the Collection of the Rev. T. Wiltshire, F.G.S. (P. 91.) 

 1 b. Upper surface of the same specimen. 

 1 c. Lateral view of do. 



1 d. Inter-ambulacral plates, arabulacral area, and poriferous zones, magnified four 

 times. 



1 e. Basal portion of an ambulacral area, magnified four times. 



1 /. Portion of a primary spine, magnified five times. 



From the Grey Chalk. 



Fig. 2 a. PsEUDODiADEMA Brongniarti, A(/assiz. Fragment of a large test, upper sur- 

 face, natural size, in the cabinet of Rev. T. Wiltshire, F.G.S. (P. 111.) 

 2 b. Under surface of the same, do. 

 2 c. Base of the ambidacral area, magnified four times. 



