PLATE XXI A. 



From the Grey Chalk. 



Pig. 1 a. PsEUDODiAUEMA ORNATUM, Goldfuss,iYom. the cabinet of the Rev. T. Wiltshire, 

 P.G.S. Upper surface, natural size. (P. 103.) 



1 b. Under surface, natural size. 



Pig. 2 fi. PsEUDODiADEMA Brongniarti, ^y«5520. British Muscum, natural sizc. (P. 1 1 1 .) 



2 b. „ „ Upper surface, magnified one half diameter 

 2 c. ,, „ Under surface, do. do. 



2d. „ „ Lateral view, do. do. 



2 e. „ „ Arabulacral area, poriferous zones, and one 



half of an inter- ambulacral area, mag- 

 nified six times. 



2f. „ „ Primary tubercle, magnified. 



Pig. 3. „ „ Spines, natural size. 



Fig. 4. „ „ Portion, magnified six times. 



