PLATE XVIII. 



Fro))i the Grey Chalk. 



Fig. 1 a. PsEUDODiADEMA VARioLARE, BroTiffnicirf. Upper surface of a large test, in 

 thecabinetof the Rev. T. Wiltshire, F.G.S. Restored, natural size. (P. 107.) 



1 b. Under surface of the same, do. Do. 



1 c. Anibulacral plate, magnified six diameters. 



From the Chloritic Marl. 



Fig. 2. PsEUuoDiADEMA VARIOLARE, Brongniart. A very perfect specimen from 

 Chard, in the cabinet of Dr. Wright, F.R.S.E. Magnified one half diameter. 



Fig. 3 a. PsEUDODiADEMA Rhodani, Agassiz. Upper surface, magnified one half. In 

 the cabinet of Dr. Wright, F.R.S.E. (P. 96.) 



.'5 h. Under surface of the same. Do. Do. 



3 c. Lateral view of do. Do. Do. 



3 d. Ambulacra, inter-ambulacra, and pores, magnified fonr times. 



3 e. Four uiter-ambulacral plates, magnified four times. 



