168 CCELENTERATA. 



tabula, and the living polyp above. In this way massive corals are formed ; the 

 secretions take place at the top, and the animal cuts itself off from the coral skele- 

 ton below. Prof. Dana says : 



" It is not more surprising, nor a matter of more difficult comprehension, that a 

 polyp should form structures of stone (carbonate of lime) called coral, than that 

 the quadruped should form its bones, or the mollusk its shell. The processes are 

 similar, and so the result. In each case it is a simple animal secretion ; a secretion 

 of stony matter from the aliment which the animal receives, produced by the parts 

 of the animal fitted for this secreting process ; and in each, carbonate of lime is a 

 constituent or one of the constituents of the secretion." 



Ordinary corals of the present seas have a hardness a little greater than com- 

 mon marble, or about equal to aragonite, and give a ringing sound when struck 

 with a hammer. 



The Anthozoa are divided into three Subclasses, two of which, Zoautharia 

 (zoon, animal; anthos, flower) and Alcyonaria (allcuoneion, a zoophyte, like the 

 kingfisher's nest),' occur in palaeozoic rocks. The Zoantharia are divided into seven 

 orders, four of which are said to be palaeozoic: viz., Perforata, Tabulata, Rugosa, 

 and Tubulosa. To the Perforata the genera Protarea and Pleurodictyum have been 

 very doubtfully referred, and the Auloporidae have been classed with the Tubu- 

 losa. All other palaeozoic corals are referred to the Tabulata and Rugosa. The 

 family Favositidae is typical of the Tabulata, and the family Cyathophyllidae of 

 the Rugosa. Authors are not in accord respecting the ordinal relations of all the 

 families, and hence we will simply arrange them alphabetically. 



CLASS ANTHOZOA. 

 SUBCLASS ZOANTHARIA. 



FAMILY AULOPORHXE. Aulopora, Romingeria. 



FAMILY CHETETID^E. Chetetes, Dania, Ptychonema. 



FAMILY COLUMNARHD^E. Calapoecia, Columnaria, Favistella. 



FAMILY CYATHOPHYLLIDAE. Acervularia, Acrophyllum, Amplexus, Aniso- 

 phyllum, Arachnophyllum, Astraeophyllura, Aulacophyllurn, Aulo- 

 phyllum, Axophyllum, Baryphyllum, Blothrophyllum, Bucauophylluni, 

 Campophyllum, Chonophyllum, Clisiophyllum, Coleophyllum, Crasped- 

 ophyllum, Crepidophyllura, Cyathophyllum, Diphyphyllum, Duncauella, 

 Elasmophyllum, Eridophyllum, Hadrophyllum, Hallia, Heliophyllum, 

 Heterophrentis, Lithostrotion, Lophophyllum, Omphyma, Pachyphyllum, 

 Palaeophyllum, Phillipsastrea, Ptychophyllum, Pycuostylus, Streptelasma, 

 Strombodes, Stylastrea, Trochophyllum, Zaphrentis. 



FAMILY CYCLOLITID^E. Combophyllum, Discophyllum, Microcylus, Palae- 

 ocyclus. 



FAMILY CYSTIPHYLLID^B. Cystiphorolites, Cystiphyllum, Cystostylus. 



FAMILY FAVOSITIDJE. Alveolites, Chonostegites, Cladopora, Coanites, Den- 

 dropora, Emmonsia, Favosites, Leptopora, Lunatipora, Michelinia, Pleuro- 

 dictyum, Pachypora, Sphaerolites, Striatopora, Syringolites, Trachypora, 

 Vermipora. 



FAMILY HALYSITLD^. Halysites. 



FAMILY PORITIDJS. Protarea. 



