142 HISTORICAL PALAEONTOLOGY. 



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

 phyllum (fig. 82), Zaphrentis (fig. 81), and Cystiphyllum (fig. 80), 

 are perhaps those most abundantly represented none of these 

 genera, however, except Heliophyllum, being peculiar to the 

 Devonian period. There are also numerous compound Ru- 

 gose corals, such as species of EridophyUum^ Diphyphyl- 

 lum, Syringopora, Phillipsastrcea, and some of the forms of 

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

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



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

 Hamilton * ormation, Canada. (After Billings.) 



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 

 honeycomb. The most abundant species are Favosites Goth- 

 landica and F. hemispheric^ both here figured, which form 

 masses sometimes not less than two or three feet in diameter. 

 Whilst Favosites has acquired a popular name by its honey- 

 combed appearance, the resemblance of Michelinia to a fossil- 



