06 MADREPOKAKIA. 



This conil is ivnotlier ilhi.slnitioii (if the giowlli priuciplc I'dnnulatcd on p. 15, that, the 

 emiucuces ou inassivo lonus luuglily rt'iioat the normal sliape of the stock it.sulf. 



51. Porites Porto Rico 6. {P. Porti-Riconis scxta.) 



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



Syn. Porites astrwoides fmma /3 Vaughan, Bull. U.S. Fish Commission, 1900, ii. p. 318, pi. xxxiii. 

 and xxxiv. fig. 2. 



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

 fewer eminences than the last and of a different sliape. They rise very gra<lually as smooth 

 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 calicles lai-ger, from 1 • 5 to 2 mm., 

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

 ai'c typical of the astneoid Porites, see p. 142, but in this case the wall reticulum is not only 

 much slighter 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. 

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

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

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

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

 rather than indii-ectly as, according to the present tendency, so many formce of an imaginary 

 species, " astrwoides." It appears to me an impossible task to say where to limit the formce 

 and where to start new species. Ur. Vaughan himself makes a new species for such a form as 

 P. Brazils 2 ( = branncri Eathb.), 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 tlie limits of 

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



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

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



Description. — This corallum rises in tlie centre of a wide exjilanate base into a low blunt 

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

 centre. 



The calicles have tliick walls of irregular woolly-looking reticulum. Ou the tops of the 

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



