58 ANEMONES AND CORALS 



interesting; they first appear in the Cambrian strata, and are 

 present in all subsequent formations. The earliest Hydrozoa, the 

 fossil Graptolites (Greek, graptos, written) are found in Cambrian, 

 Ordovician, and Silurian strata, as slender colonies shaped like a 

 quill pen. A great group of Corals, the Rugosa, which nourished as 

 reef-builders in the Palaeozoic age, have their modern representa- 

 tives in the small Guynia and Duncania of the floors of the Medi- 

 terranean and the Atlantic Oceans. The Aporosa and Perforata, 

 faintly foreshadowed in Palaeozoic ages, increased in importance 

 in early Secondary times ; and the Tubipora, to which the Organ- 

 pipe Coral belongs, are probably of great antiquity, for there are 

 forms like them to be found in the Devonian rocks. The Oolitic 

 age had its great reef-building Corals, and the chalk contains 

 beautifully preserved remains of a fauna which closely resembled 

 that of the deep seas of the present day, while many genera of 

 Tertiary Corals still exist. 



