56 



HALF AN HOUR WITH SPONGES. 



appears to be the oldest, having been found in 

 the formations just mentioned. They were very 

 Fig. 18. abundant during the 



Cretaceous epoch, 

 including those ele- 

 gant fossils known 

 as "Choanites " 

 and Ventriculites. 



Our British 

 sponges belong- to 

 the horny (or Jcera- 

 tose) and the cal- 

 careous groups. 

 As we have already 

 remarked, those 

 living at low water 

 are very small and 

 insignificant, their 

 bright colours alone 

 rescuing them from 

 utter contempt. To 

 find them, you must 

 go to where the rocks 

 jut out furthest to 

 sea; and here, at low 

 water, you will see 

 in* the upper parts 

 of the miniature 

 caverns which may 

 be formed in them, 



Mag. X 200. 

 Fig. 19. 



Mag. X 100. 



