﻿ON 



THE STRATIGRAPHICAL DISTRIBUTION 



OF THE 



OOLITIC ECHINODERMATA.* 



All the classes of the animal kingdom, when viewed in relation to their stratigraphical 

 distribution, are not of the same value to the palaeontologist. Some Mollusca, as the 

 Conchifera and Gasteropoda, have a much greater extension in time than the Cephalopoda, 

 and among Radiata, the Echinodermata and Anthozoa may be adduced as examples of 

 classes whose life was alike limited ; in estimating the value of palseontological evidence, 

 therefore, it is necessary to take into consideration this important fact, which has not 

 received the attention it is so justly entitled to. 



The Echinodermata, although occupying a low position in the animal series, in a 

 zoological point of view, still afford the palaeontologist most important data for discussing 

 questions relative to the distribution of species in time and space ; it is well known, for 

 example, that the Silurian, Devonian, and Carboniferous rocks are all characterised by 

 distinct forms of Crinoidea, most of which are limited in their range to the different 

 stages of these great groups. It is the object of this chapter, however, to show that the 

 species of Oolitic Echinodermata had a like limited range in time, and that the different 

 stages of the Oolitic formations are characterised by species which are special to each. 



Dr. William Smith was doubtless aware of the value of the Echinodermata in strati- 

 graphical geology, for he carefully noted the different species known to him which 

 characterised the different subdivisions of the secondary rocks ; and it is a remarkable fact, 

 in connection with this subject, that although our knowledge of the species of this class 



* The stratigraphical distribution of the Echinodermata, originally written for this work, was commu- 

 nicated, in the form of a memoir, to the Geological Section of the British Association, at the meeting held 

 at Cheltenham, in August, 1856. The Council did me the honour, to order the communication to be 

 printed entire among their Reports ; for this reason it appeared in the ' Report of the British Association 

 for the Advancement of Science for 1856,' and is now corrected down to the present date. 



