GONIOPOEA. 23 



portion of the skeleton which is still supporting the living colony from that portion which the 

 living tissues have abandoned. They may be very thin and often incomplete, but, like the 

 epitheca, they are a constant factor in this genus. In PI. III. fig. 2, they can be seen as faint 

 curved lines running across the picture. 



The Growth-Forms. — With a parent calicle such as we have sketched for the primitive 

 Goniopora, with low thick walls and shallow fossa, great plasticity of colony formation 

 was hardly to be expected. The normal symmetrical budding of such a calicle could 

 only result in the formation of circular, slightly convex astrseiform colonies. This was, 

 therefore, the simplest and most primitive growth-form, and is exemplified by several 

 fossil and recent members of the genus, while all the other known forms may be 

 deduced from it. 



The term "astrseiform" is used deliberately. For the real distinction between an 

 astrseiform colony and other forms depends entirely upon the shape and growth of the 

 individual caUcles. If the parent calicle is capable of independent growth in height and can 

 bud laterally above the substratum, branching forms will arise. These, as in the case of 

 Astneopora* may become massive by secondary submergence in ccenenchyma. But when 

 neither the parent nor any daughter calicle is capable of independent growth in height, and all 

 the buds have to develop either upon the flattened epitheca or in accidental interstices, and in 

 the latter case are never able to rise independently above the general level, then we have an 

 astrseiform colony. Probably every one of the fundamental variations on the primitive skeleton 

 of the Stony Corals has at one time or another produced its astrseiform colonies. Many indeed 

 seemed incapable of producing any other form of colony ; hence the great numbers of the 

 so-called Astrccidcc, which will only be correctly classified when we have analysed the different 

 structural types of their component calicles. 



So far as growth-form is concerned, Gonioimra (and Porites) may be regarded as astrseiform 

 perforates.! 



Starting from what we have described as the primitive form of colony, viz. the circular 

 slightly convex astrseiform stock which would result from the normal budding of the primitive 

 parent calicle, we find two clear lines of departure from tliis primitive form.f 



(a) They have become less convex, and growth has gone on round the edges, and the colony 

 has become explanate. 



(b) They have become more convex, and the colonies have become hemispherical and 

 columnar. 



Both of these have again produced secondary modifications, which we shall now have to 

 consider, but before doing so we would point out that both these two principal diverging lines 

 of colony formation coincide with two diverging types of calicle, and we are face to face with 

 the problem, which variation depended upon which ? Did the growth-form take the lead 



* Ann. Mag. Nat. Hist. (6) xx. (1897) pi. ii. fig. 4. 



f Compare Fromeiitel's name for the Poritid», " Polyastrees Perfores " [•<;<■], mentioned on p. 5. 

 f For a more detailed division of the growth-forms than that here briefly sketched, see 

 Table III. p. 169. 



