218 HIDDEN BEAUTIES OF NATURE 



even the microscopic spicules of the flinty chain- 

 armour which were embedded in the ancient crea- 

 tures' fleshy substance can now be detected in the 

 layer of flint after it has been thinned down and 

 polished (fig. 58). Here are two flints broken open 

 to show the nucleus in each instance (see chapter on 

 Euplectella). These flinty specimens are known as 

 ventriculites, and were quite an enigma to our geo- 

 logists, until the ' Venus's flower basket' was brought 

 to this country from the depths of the Philippine 

 Seas. 



What was thought to be an extinct organism was 

 found to have plenty of representatives. It may be 

 so in the case of the choanites. 



Here are traces of other forms of the sponge 

 family embedded in the chalk. These must be taken 

 home and carefully worked out with all the patience 

 you can command. They will well repay any trouble 

 expended upon them. There are also some small 

 corals well worth our attention. In this stream 

 coming out from the base of the cliff we shall find 

 tiny ammonites, all of which are replaced by the 

 prevailing iron pyrites. Collectors frequently have 

 them mounted as trinkets. 



This is a fragment of a lovely fossil sponge. Mr. 

 Toulmin Smith, some years ago, found sufficient of 

 this kind of sponge to construct a very splendid 

 specimen (fig. 59). The creature had wing-like 

 appendages radiating from a central tube or funnel, 

 and was furnished with roots and anchoring appa- 



