24 OUR COMMON BRITISH FOSSILS. 



Generally, however, they are of a stony character 

 and solid everywhere, except in the pure white 

 chalk. 



The Ventriculite family of sponges are hexactinellid^ 

 and their shapes and structures are often very beau- 



Fig. i8.— Ventriculite. 



tiful, a slight magnifying power showing a similar 

 latticed appearance to that we admire so much in 

 the modern " Venus' flower-basket " {Etiplectelld). In 

 the white chalk of Sussex, Wiltshire, and Norfolk, 

 Ventriculites occur in great numbers. Ventriculites 



