CHAP. X.] 



CONTINUITY OF THE CHALK. 



485 



of ' spicules of the sarcode,' one large, C-shaped, the 

 other much more minute, answering to Bowerbank's 

 6 tridentate equianchorate ' type ; every now and then 



FIG. 82. Ventrievlites simplex, TOULMIN SMITH. Section of the outer wall, showing the 

 structure of the silicious network, (x. 50.) 



the rind thus formed coming to the margin of a small 

 pore. The interior of the sphere is filled with soft 

 semi-fluid sarcode, supported by the loosest possible 



> 



FIG. M.Ccrlnsplirrra tubifex, Wvviu.E THOMSON. Slightly enlarged. Oft tho coast of Portugal. 



mesh-work of granular horny matter and pin- 

 headed spicules. Prom points apparently irregularly 

 placed on the surface of the sponge, tubes about 

 3 mm. in diameter run out in all directions; 

 the walls of the tubes are thin and delicate, being 



