DlSTIilBUTION OF GROVVTH-FOKMS. 131 



built up of series of such colonies are naturally numerous, but tliey pass with massive forms, 

 and we meet at the outset with the difficulty mentioned above — are we to classify according to 

 the form of the initial colony or by the stocks which they build up ? If, for example, we find 

 a small plano-convex colony, how are we to know whether it is an adult stock or merely the 

 initial segment of a stock ? With these doubts kept well in mind, we find the following West 

 Indian and Atlantic forms showing, either in their complete forms or in their initial colony 

 units, this simple character. 



P. West Africa 1. Grows in small flat convex patches apparently on mud. 



P. Awjuilla 2. The small stock is nearly plano-convex and it appears to be built of 



colonial units of that shape. 

 P. Santa Cruz 1. Perhaps only a young stage. 

 P. St. Thomas 5. Entangled with branching forms, but may be regarded as built of 



plano-convex colonies (? belongs to B, c). 

 P. St. Thomas 6. " Placentiform," with edges partly free (? belongs to B, c). 

 P. West Indies x. 15. EoUed round the stem of a Gorgonid. 



N.B. — It may be that the characters of the calicles might enable us to say whether 

 the individual plano-convex colony was destined to form a massive or an explanate adult. 

 This appeared to be the case in the genus Goniopora. Shallow calicles are characteristic of 

 explanate forms, and deep calicles of massive forms. 



B. Explanate. 



The same remarks hold good again here. Are massive forms which are obviously built 

 up of piles of thin layers to be classified aS thin explanate or as massive ? We propose to 

 mention them under both headings, but at the same time we note that Porites whose initial 

 colony units are thin layers, need not necessarily build massive stocks. They may build 

 loose crusts, or, again, if the lateral growth is very vigorous, the successive growths may start 

 into being at the edges and not in the centre of the parent colony. In this way we obtain 

 expanding disk-like growths dying away in the centre. This kind is seen, for instance, when 

 the original colony grows out laterally from a side like the basin of a drinking-fountain (see 

 below for an example Porites x. 10, p. 137). 



a. Thin, encrusting. 



P. Cape Verde Islands 2. Forms, by successive thin layers, a small cushion-shaped 



mass. 

 P. Guadalupe 3. Apparently creeping over the ground. 

 P. Barhuda 3. A small cushion-shaped mass, built of thin layers. 

 P. West Indies x. 25. A thin layer built up of several tliinner layers. 



b. Thin, with free edges. 



P. AntigvM 4. Thin layers build up an agaric-shaped mass (? belongs to C). 

 P. West Indies x. 29. ( = " Neoporites Ajaricus," D. and M.). 



c. Thick, encrusting. 



P. Cape Verde Islands 1. With stout spreading lobate edges. 

 P. Brazil 2. Closely encrusting, and with convex surface (? A). 



s 2 



