14 MADREPORARIA. 



" species." There is no justification for the implication that they have no taxonomic problems 

 of sufficient importance to trouble about. It is true that this has been the main drift of the 

 work done on these forms until recent years, but, as stated in the historical sketch, our 

 contention is that this conclusion is not based upon a close enough study of the facts, which 

 could never be seen for themselves, but always through a haze of imaginary species. The 

 problems are probably of greater interest and intricacy simply because they are thus circum- 

 scribed within narrower limits of variation. 



The Growth-Forms. — We may again, as in the C£ise of all the Poritidse, start from small, 

 slightly convex, " astrseiform " * colonies as the first result of the budding of the parent, which 

 forms the first " colonial unit " in the building up of the ultimate stock (§ IV. p. 20). All the 

 subsequent growth-forms can be deduced from this, in the first place, according to the 

 different rates of growth of its several regions : — if the edges grow alone, we have thin expanding 

 forms ; if the central regions grow alone, we have columns which may fork and branch : 

 and in the second plfice, according to the way these colonial units multiply. 



From the historical account above given it would appear as if these possible growth-forms 

 were, in fact, extremely limited ; confined to massive cakes (asirceoides of Authors) and to 

 branching forms called clavaria,/urcata, etc. It is true that they are limited as compared with 

 the marvellous wealth exhibited by the genus in the Indo-Pacific area with their smaller calicles, 

 and more plastic (because more delicate) skeletal frameworks ; at the same time they are not so 

 limited as has been supposed ; and, further, when more localities have been studied, it is to be 

 expected that their range will be still greater than that which the following scheme can show : — 



1. Expanding forms — 



a. Thin, with edges creeping over the substratum. 



b. Thicker, with convex or raised centres. 



c. Thick hemispherical or conical mounds. In these last the growth of edges 



and centre must be nearly equal. 



2. Forms which start as expanding bases, from the surface of which one or more 

 branching, or merely dividing, stems rise up later. 



3. Forms the centre of which rise up at once as single stems upon disk-shaped bases. 

 The stems fork, and, by multiplication of segments (see below, p. 20), produce branching stocks. 



4. Forms which seem to rise up at once into egg- or pear-shaped stocks, and divide 

 irregularly ; the divisions are carried on by metameric growth, and continue to swell as they rise. 



Examples of all these are to be found among the specimens described in this Catalogue (see 

 Table III. p. 130) ; while if we study Table II. we see how small is the area from which they 

 have been gathered, and may thence reasonably infer that many more may ere long be added. 



This scheme is already a great advance upon the results hitherto arrived at by the 

 systematic work of my predecessors in this field, and it is an advance in the direction of closer 

 analysis, while the discovery, made since this was first written, that these corals are built 



• On the use of this term in this connection, see Vol. IV. p. 23. 



