I04 AN INTRODUCTION TO THE STUDY OF FOSSILS 



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A 



Fig. 37. — Comparison of a fossil and a modern glass sponge. A, internal mold of 

 Prismodictya prismatica Hall; very abundant in the ocean covering New York 

 state during the Upper Devonian time. Natural size. B, the siliceous skeleton 

 of Venus' flower basket, Euplectella, about a foot high, living in the East Indian 

 seas. 0., osculum, the opening of the large central cavity {p.c) now partially filled 

 with mud. At the junction of the principal bands of spicules (sp.b.) were probably 

 tufts of spicules, the bases of which have left their impressions (sp.t.) upon the 

 internal mud mold. Prismodictya was probably attached to some foreign object 

 by a flattened area at o. A modified from Hall and Clarke. 



