Prototheca of the Madreporaria, 27 



like those shown in diagrams figs. 14 or 15, and from It the 

 dissepiments slope away on the one side into and across the 

 calicle, and on the other down to tlie substratum. But it is 

 doubtful whether an actual section of the wall would sliow 

 that structure so straight and continuous as it is shown 

 diagrainmatically in the figure (15), and it is quite certain 

 that the tabulae would not be so regular and complete. 



It was some such case as that just referred to (?a specimen 

 of Acarithastrcea), in which vesicular arched walls separated 

 calicle from calicle, that inspired the diagram given by me on 

 pi. xxxiii. fig. 10 in vol. xxvi. of the 'Journal of the Linnean 

 Society of London.' I am not yet, however, prepared to 

 answer the question as to which of the two metliods of edge- 

 zone formation we have just been comparing — that of fig. 13 h 

 or of fig. 15 — the actual case was due. For, as we have 

 just seen, the Lithophrjllice show that the smooth, arched, 

 vesicular dissepimental wall might be a secondary modifica- 

 tion, and due to colony formation, of the true edge-zone 

 formation of fig. 11, which is the subject of this section. 



V. Early Budding and Colony Forntation. — In vol. iv. of 

 the ' British Museum Madreporaria,' Introduction, p. 23, I 

 suggested a restricted use of the word " astra^iform," viz. 

 to colonies of calicles all reaching to the same height and 

 without any apparent tendency to grow and bud independently. 

 The true asfraiiform colony is therefore that built up by a 

 calicle which is by habit low and whose buds spread laterally 

 over the substratum all round the parent. The grou]) 

 Aslraidw as now understood consequently cannot be a natural 

 one. It appears to me that we may have astrisiform colonies 

 of corals whose protothecae are modified upon very different 

 plans. And it is on these modifications of this fundamental 

 element that the ultimate classification will have to be based. 



We might expect, then, a great development of astraiiform 

 colonies among the Palajozoic corals from the forms in which 

 the prototheca was early flattened out in the ways described. 

 We might also expect that it would be those methods of 

 fiattening out which were from the first symmetrical;, because 

 if the parent had acquired its flattening as a secondary 

 matter, after having perhaps at one time fallen over, it could 

 hardly be expected that the buds would appear with the 

 necessary flattened symmetry straight away, although in some 

 of the Astrffiid forms with very large calicles this must 

 apparently have taken place. 



While I think these conclusions are perfectly justifiable, 

 we learn from the researches of Lindstrom that one great 

 group of Palaeozoic astrteiform corals with very small calicles^ 



