CHAP. X.] 



CONTINUITY OF THE CHALK. 



485 



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

 other much more minute, answering to Bowerbank's 

 ' tridentate equianchorate ' type ; every now and then 



Mrmrmr 



Fig. S2 — Ventriculites simplex, Totjlmtn 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. 83. — Cmlosphiera tubifex, Wvville Thomson. Slightly enlarged. Off the mast of Portugal. 



mesh-work of granular horny matter and pin- 

 headed spicules. Erom 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 



