30 PICTURESQUE SKETCHES 



structure would, probably, enable them to live 

 through many changes, since they could adapt them- 

 selves to altered conditions of temperature and posi- 

 tion, at times when almost every other animal was de- 

 stroyed; and, accordingly, in the species of them 

 found fossil, there is far less difference from existing 

 nature than is the case with any other creatures. 

 These little corallines, and the larger and more im- 

 portant group of true corals, as they commenced ex- 

 istence so early, seem also to have been comprised 

 within a very limited number of natural families, and 

 some particular species probably extend completely 

 through the whole number of beds of the first great 

 epoch. 



Amongst the earlier forms are those of the genera 

 Aulopora (3) and Catenipora (4, 5), all belonging 

 Fig. 3 to the group of lowest 



organization among co- 

 ralline bodies, and hav- 

 ing the most solid stony 

 or horny framework. 

 They are radiated and 

 star-like in their struc- 

 ture, have no true in- 

 SIMPLK FLOWER-LIKE CORALLINE. testinal canal, and in 

 (Aulopora). many, though by no 



means all the species, the animal is capable of locomo- 

 tion. The species figured 3 is common in rocks of the 

 older palaeozoic period, and is closely analogous, in 

 many respects, to species yet inhabiting tropical and 

 southern seas. The chain coral (4, 5) offers another 

 and a beautiful example of this peculiar structure, and 

 being a fossil exceedingly common in some silurian 



