I04 AN INTRODUCTION TO THE STUDY OF FOSSILS 



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 a. A modified from Hall and Clarke. 



