92 MADREPORARIA. 



septal rows, and very irrc^nilarly into coiic.oiilric riii<,'s. Tliu iiKisl conspicuous of Uicse rings 

 has twelve granules, which may, perhaps, be regarded as the " septal" granules ; but the rest 

 of the granules, viz. those which might be regarded as pali on the inside, and wall granules on 

 the outside, are too confused for us to be able to uiuavfl the elements with any satisfaction. 

 The fos.sa is deep, and its base is filled up by flaky tissue showing no .symmetry. 

 The colour of the unbleached coral is a cold dark gi'ey. 



This coral is interesting as being one of the few West Indian PorUes wliicli show any 

 a])])roach to being ccencnchymatous, cf 1'. Bahamas 1, p. 76. Parts of other exjjlanate West 

 Indian Pnrites sliow great thickening of the walls, ,see Table IV. A, p. 139, but this is, so far, 

 the only form in wliich tlio wall proliferation extends over the whole stock, and is so 

 pronounced. 



There are traces of five stocks of this PoriteK scattered over the Gorgonid skeleton. The 

 one figured is the largest intact specimen. Two others, which at one time grew round the 

 stems, have since l)ecn overgrown by the branching forms ; see the two descriptions following. 



Underneath the explanate root-ljase of the Gorgonid, which had been overturned, two 

 small, flat, explanate stocks of the same kind, apparently unable for some reason or other to 

 fuse, sought to overlap one another. This is what one would expect, because though fusions 

 of hranches certainly take place here and there, it is of interest to note that it is far more 

 frequently avoided. 



In view of the recent tendency to claim all the explanate West Indian forms as of one 

 and the same species, astrmoides, this specimen is welcome as enabling us to take some 

 decided stand against such a purely theoretical limitation. 



a. On a Gorgonid skeleton in five small stocks. Zool. Dept. 43. 3. G. 98 (part). 



The other Pontes upon the Gorgonid were originally placed under separate headings, for 

 they appeared to be very different (cf PI. V. figs. 3, 4). On revision, however, I believe 

 they may be regarded as two variations of the same. They hardly admit of being described 

 together, and consequently the two descriptions are now included under the same heading. 



81. Porites West Indies j:. 16. {P. Americana inccriw scdis seidadccima.) 

 (PI. V. figs. 4, 5 ; PI. XVII. figs. 20 /3, 20 y.) 



[British Museum.] 



This coral encu'cles the Gorgonid skeleton, anil wlien securely fixed, grows up into short, 

 thick, branching lol)es. Of the two specimens, one of them, a, has only just begun to rise into 

 branches which have been unfortunately broken off, while tiie other, b, has developed lobes. 



Description. — The corallum spreads as an explanate creeping base, which encu-cles the 

 stems of the Gorgonid skeleton, enveloping at the same time other encrusting corals. The 

 edges are stout but sharp. From its surface processes arise, the shapes and methods of 

 branchings of wliich are unknown. 



The calicles (on the base) are 1-5 nun. in diameter, mostly polygonal, .shallow but 



