FLORIDA REEFS. 61 



AsTR/EANs: tentacles not definitely limited in number, though usually not exceeding one hundred, and 

 generally much below this number; transverse floors. Mseauclrinas, generally referred to Astraeans, 

 are higher than the true Astra;ans, on account of their compound Polyps. 



Fungid^'E: indefinite multiplication of tentacles ; imperfect transverse beams. 



AcTiNi/E : indefinite multiplication of tentacles ; soft bodies and no transverse beams. 



If now we compare this structural gradation among Polyps with their 

 geological succession, we shall find that they correspond exactly. The fol- 

 lowing table gives the geological order in which they have been introduced 

 upon the surface of the earth: — 



GEOLOGICAL SUCCESSION. 



Present, Halcyonoids. 



Pliocene, \ 



Miocene, V Madrepores. 



Eocene, ) 



Cretaceous, 



Jurassic, 



Triassic, 



Permian, 



Carboniferous, ) 



Devonian, [ Fungidse. 



Silurian, ' 



With regard to the geological position of the ActiniaB we can say nothing, 

 because, if their soft, gelatinous bodies have left any impressions in the 

 rocks, none such have ever been found ; but their absence is no proof that 

 they did. not exist, since it is exceedingly improbable that animals destitute 

 of any hard parts could be preserved 



Porites 



and 

 Astrteans. 



