Fig 9 Sponge spicules (skeletal), a, monaxonid, Halichondna pamcea, 

 Recent. 6, tetractinellid, Paekastrella, Upper Greensand. c, te- 

 tractinellid, Geodites, Eocene, d, lithistid, Scytaha radiciformis, 

 Chalk e, lithistid, Seliscothon mantelli. f, hexactinelhd, Ccelop- 

 tychium agaricoides, Chalk, g, octactinellid, Astneospongia, Silurian. 

 ft, heteractinellid, Asteractinella expansa, Carboniferous, j, calci- 

 sponge, Grantia compressa, Recent. All magnified. 



