A MONOGEAPH 



ON THE 



FOSSIL ECHINODERMATA 



OF THE 



OOLITIC FORMATIONS. 



Sub-Kingdom— RADIATA. 



This great division of the Animal Kingdom includes classes which differ widely from 

 each other in form, organization, and habits. Some have the body circular, globular, or 

 ringed ; or vermiform, plant-like, or amorphous. Some are enclosed in a soft arachnoid, 

 transparent membrane, and float like crystal masses through the water, as the Infusoria and 

 AcalepluB ; others hang like living stalactites from the roofs of submarine caverns, like the 

 Amorphozoa ; or, assuming the forms of the Vegetable World, they develope ramose stems, 

 with numerous branches, of which myriads of zoophytes are at once the builders and 

 inhabitants, as the Polypi/era. Some are enclosed in exquisite shells, microscopic in size, 

 but unrivalled in symmetry, although the structure that produces them is but a mere film 

 of jelly, as the Foraminifera ; others have a complicated calcareous skeleton, composed of 

 many thousands of separate elements, which, for beauty and contrivance, is unsurpassed by 

 that of any other class, as the Echinodermata. Where the nervous system has been dis- 

 covered, it consists of a simple gangliated filament, surrounding the entrance to the 

 digestive organs ; but in by far the greater number of animals grouped in this division, 

 no distinct nervous system is found, although the creatures themselves possess an exquisite 

 sensibility. 



The sub-kingdom Radiata is formed of classes which are more remarkable for their 



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