144 HISTORICAL PALAEONTOLOGY. 



server the most minute details of their organization. As before, 

 the principal representatives of the Corals are still referable to 

 the groups of the Rugosa and Tabulata. Amongst the Rugose 

 group we find a vast number of simple " cup-corals, " generally 

 known by the quarrymen as " horns, " from their shape. Of 

 the many forms of these, the species of Cyathophyllum, Helio- 

 phyllum (fig. S2),Zaphrentis (fig. 81), and Cystiphyllum (fig. 80), 

 are perhaps those most abundantly represented none of these 

 genera, however, except H elio phyllum , being peculiar to the 



Fig. 83. Portion of a mass of Crepidophyllum ArcMaci, of the natural size. 

 Hamilton Formation, Canada. (After Billings.) 



Devonian period. There are also numerous compound Ru- 

 gose corals, such as species of Eridophyllum, Diphyphyl- 

 lum, Syringopora, Phillipsastr&a, and some of the forms of 

 Cyathophyllum and Crepidophyllum (fig. 83). Some of these 

 compound corals attain a very large size, and form of them- 

 selves regular beds, which have an analogy, at any rate, with 

 existing coral-reefs, though there are grounds for believing that 

 these ancient types differed from the modern reef-builders in 

 being inhabitants of deep water. The " Tabulate Corals " are 

 hardly less abundant in the Devonian rocks than the Rugosa; 

 and being invariably compound, they hardly yield to the latter 

 in the dimensions of the aggregations which they sometimes 

 form. 



The commonest, and at the same time the largest, of these 

 are the " honeycomb corals, " forming the genus Favosites 

 (figs. 84, 85), which derive both their vernacular and their 

 technical names from their great likeness to masses of petrified 



