66 MADREPORARIA. 



This coral is another illustration of the growth principle formulated on p. 15, that the 

 eminences on massive forms roughly repeat the normal shape of the stock itself. 



51. Porites Porto Rico 6. (P- Porti-Biconis sexta.) 



[Porto Rico, coll. Vaughan ; U.S. National Museum.] 



Syn. Pontes astrceoides fmina ft Vaughan, Bull. U.S. Fish Commission, 1900, ii. p. 318, pi. xxxiii. 

 and xxziv. fig. 2. 



Description. — The corallum is massive and more plano-convex than hemispherical, with 

 fewer eminences than the last and of a different shape. They rise very gradually as smootli 

 gently sloping plano-convex mounds, separated by concave valleys here deep and narrow, 

 there broad and shallow. 



Over the mounds the calicle walls are thicker and the caUcles larger, from 1 • 5 to 2 mm., 

 whereas on the smoother intervening valleys they are only 1 mm. in diameter. The calicles 

 are typical of the astrfeoid Porites, see p. 142, but in this case the wall reticulum is not only 

 much sligliter but tends to be more flaky. The septa are slender points, long or short, and not 

 showing any conspicuously radial arrangement. 



This description is again taken from Dr. Vaughan's text and photographs. Once more, in 

 giving it a separate place, I do not say that this is of a different species from that of the coral last 

 described. I simply describe it as a very distinct and definite form assumed by Porites. 

 Wliat is more, it can be shown that the differences which characterise these " P. Astrceoides" 

 are definable and illustrate a principle of growth not hitherto recognised. But even apart from 

 this principle, a glance at Table III. p. 130, shows us that the expanding and massive 

 forms fall into natural divisions. These divisions might just as well be recognised directly 

 rather than indirectly as, according to the present tendency, so many formce of an imaginary 

 species, " astrceoides." It appears to me an impossible task to say where to limit the formm 

 and where to start new species. Dr. Vaughan liimself makes a new species for such a form as 

 P. Brazils 2 {= hranneri Rathb.), and would certainly point to the differences between the 

 calicles of that form and those typical of the astrseoid group. I feel sure, therefore, of Dr. 

 Vaughan's support in the limitation of the use of that term here suggested, see p. 142. My 

 method of designation frees us from having to attempt to express opinions as to the limits of 

 species, at least at this early stage of the inquiry. 



52. Porites St. Domingo 1. (P. Bomingonis prima.) 

 [Gonaive Island, coll. Prax ; Paris Museum.] 



Description. — This corallum rises in the centre of a wide explanate base into a low blunt 

 cone, which itself consists of jagged conical peaks sloping in serrated angular ridges from the 

 centre. 



The calicles have thick walls of irregular woolly-looking reticulum. On the tops of the 

 ridges, they appear to be so tliiok as almost to close the apertures of the calicles. Just below 



