U MADRErORAEIA. 



where they appear to open on both sides, it is because two fronds of the corallum are fused 

 back to back. 



Comparison with related genera Madrepora and Astrwopora. — This description enables us 

 to compare the tyiiical growth of a Turbinariau with that of a Madrepore. In both cases we 

 have an axial polyp, round which the buds appear laterally. But in Turbinaria we have 

 only one true axial polyp, which gives off only one ring of daughters ; these themselves 

 l)ud, and their buds again bud, and so on. If, as above hinted, these daughters are to be con- 

 sidered in their turns as axial polyps which give off parts of rings of buds, they again give 

 off only one ring or part of a ring each. In Madrepora the first axial polyps give off 

 numerous tiers of daughters, any one of which may become in its turn an axial polyp, giving 

 off again numerous tiers of daughters, and so on. 



A comparison with Ast7'a;opora, with which the genus Turlinaria is usually closely asso- 

 ciated, will be found in the Introduction to the Catalogue of that genus, later on in this 

 volume. We may here confine ourselves to stating that the method of budding of that genus, 

 in which no axial polyp can be <Iistinguished, is quite distinct from that of the Turbinarians, 

 and the usual association of the two genera has very little real evidence in its favour. 



GEOGRAPHICAL DISTRIBUTION. 



According to the records, the Turbinarians seem to be more or less confined to the Indo- 

 Pacific Archipelago. They occur all round the northern half of Australia, among the West 

 Pacific Islands. In the Chinese seas, as far north as Formosa ; through the Malay seas into 

 the Indian Ocean ; also in the Red Sea, and along the east coasts of Africa. I have found no 

 record of any specimen from the coral regions of the Atlantic, or from the Eastern Pacific* 



A GENERAL REVIEW OF THE VARIATIONS OF FORM AND STRUCTURE ASSUMED 



BY TURBINARIANS. 



The Variations in the Shape of the Corallum. 



Inasmuch as all Turbinarians commence life as cups, the early stages of growth may 

 be but very briefly considered. Certain variations of form appear even in the youngest 

 cups. They may be either concave or flat ; their stalks may be either tail, thin and graceful, 

 or short and thick. Further, the margin of the cup or plate may be thick or thin, but 

 this depends largely upon the size of the individual calicles. 



The most striking variations of form, however, occur as soon as the corallum has passed 

 through the early cup stage. Examination and comparison of the specimens in the National 

 Collection reveal eight different types of growth, which serve to divide the specimens, albeit 

 somewhat arbitrarily, into as many groups. 



* References to the only recorded fossil Turbinarians will be found in the note, p. 56. 



