UNKNOWN ATLANTIC OR WEST INDIAN PORITES. 91 



composing the intra-caliculai- skcluluii. The culoiu- ui' Llic uublcaclicd coral is a ricli, warm 

 red-brown. 



The section shows a very open, axial reticulum of streaming flakes, gradually thickening 

 into an irregular, closer, but not dense, cortical network of thick skeletal elements which are 

 thick right to the surface, except in the younger paits which consist mostly of the axial 

 reticulum. 



This coral, with its rich red colour, its apparently regular, dichotomous forking — each fork 

 justi twisted on its own stem — is typically West Indian in every detail of its growth. It 

 is unlike any other in the collection. It is unfortunately rather young, and it is to be 

 regretted that the effect of the twisting of the forkings cannot be followed on an older stock. 

 That this twisting is not accidental is obvious, because it occurs in each case, that is in the first 

 and second forkings, and traces of it can be seen in the third which is just commencing. 



But for this twisting, it would be the most perfect case of symmetrical dichotomy yet 

 recorded. This raises the questions as to how often we ever get the true, normal growth of 

 any coral ? Are not most of them interfered with by currents and foreign organisms, affected 

 by their positions, on which depend the physical conditions with regard to light, gravity, 

 density of water, etc. ? 



a. Zool. iJept. 39. 3. 29. 8. 



80. Porites West Indies x. 15. (P. Americana inccrtcc scdis quintadccima.) 

 (I'l. V. fig. 3 ; PI. XVII. fig. 20, a.) 



[British Museum.] 



This Porites grows upon a fragment of a Gorgomd skeleton ; it is one among a group of 

 corals — both Porites and Astrmids — scattered about upon the same object. The other Porites 

 appears to be different from this. It is at first somewhat surprising to find two or possibly 

 three different Porites growing together and yet so distinct. The natural suggestion is that 

 currents may have swept great numbers of coral larvte through the open branchwork of 

 the Gorgonid skeleton, and several different kinds have managed to attach themselves to it. 



Description. — The corallum forms small smooth colonies, which may encircle the stems of 

 the Gorgonid skeleton, or on a flat surface remain thin and explanate, that is, show no con- 

 vexity, even when as much as 1*5 cm. across. The edges are very thin. 



The calicles from median wall-thread to wall-thread are 1'5 mm. in diameter, and, but 

 for the small gradually incurving fossae, superficial. The walls, or rather the interfossal tissue 

 is thick and smoothly round-topped, curving upwards out of one fossa down into the next. 

 To the naked eye a faint median wall-thread or line appears. ' Magnification, however, shows 

 it to be only an an-angement of the sharp angular wall granules somewhat straighter than else- 

 where. When the top granules are rubbed off, the reticulum is seen to be composed of flakes, 

 mostly horizontal but tilted, deeply incised and perforated, though sparsely, with small round 

 pores. At the surface the granules show traces of being aiTanged fairly regularly into radial 



N 2 



