201 



ECHINODEEMATA. 



Clypeus Plotii, Leske. Acrosaleniabemicidaroides, Wright. 

 Nucleolites clunicularis, Llhyiud. >> spinosa, Agass. 



" orbiciilaris, Phil. Pseudodiadema depressum, Besor. 



Holectjrpus depressus, Lamk. Pygunis Michelini, Cotteau. 



Nearly all the Conchifera in the above list are likewise found 

 in the zone of Ammonites ParTcinsoni, Inferior Oolite. They 

 lived in the seas that deposited the Minchinhampton series, 

 and passed into those of the Combrash. Several of the 

 Brachiopoda are special to this formation, others have a wider 

 range. All the Echinodermata made their appearance in the 

 Parkinsoni zone of the Inferior Oolite, where they attained 

 their most perfect development; some of the species became 

 dwarfed in the Great Oolite seas, and again assumed their 

 pristine condition in the Cornbrash; indeed, it would appear 

 that the Parkinsoni zone of the Inferior Oolite and the 

 Cornbrash had many conditions in common, as proved by the 

 life-vigour of the same forms in both. 



When studied, as a whole, we find veiy few species 

 characteristic of the Great Oolite group, special to any of 

 its sub-divisions, although the same species is found to assume 

 certain varieties in the different beds in which it recurs ; an 

 evidence that the several members of the group were deposited 

 under many changes of physical conditions. 



The two sub-divisions of this series that have hitherto given 

 rise to most discussion in our attempts to correlate these strata 

 are the Fullers Earth and the Bradford Clay, which exhibit 

 considerable variety as to presence, development, and fossils. 

 These two deposits more properly belong to that class of beds 

 which the Germans wotJd call "einlager," or beds inconstantly 

 interposed between others that are more permanent members 

 of a group. In this sense these two clay beds would be 

 *'einlagers" of the upper division of the Lower Oolites. Thus 

 Ostrea acuminata, Ceromya plicata, Avicula eehinata, Pholadomya 

 Heraulti, Pecten vagans, and Pygurus Michelini, found in the 

 Fullers Earth, occur in all the other beds of the group. The 

 Stonesfield Slate is not a constant member of the series, and 



