79 



portion of the disengaged bodies, varying in the roughness of their 

 surfaces, bear a strong resemblance to the gemmules of some sponges, 

 which are of course known to be the rudimentary sponge, has led me 

 to the belief that they also are but rudimentary forms of some animal 

 or animals in a progressive state of developement, and that what- 

 ever connexion they may have had with the matter once occupying 

 the place of the flint, they certainly appear to have no natural con- 

 nection with Xanthidia, so called, of our freshwater ponds. 



EXPLANATION OF PLATE IX. 



Figs. 1 to 16. Various forms of Xanthidia, magnified 260 linear. 



Figs. 10 a, 11 a, 15 a. Ditto, „ 460 „ 



Fig. 17.) ( „ 260 „ 



Fig. 18. I Three Polythalamia, „ 260 „ 



Fig. 19. J ( „ 460 „ 



Fig. 20. A minute coralline (?) „ 140 ,, 



