36 MADREPORARIA. 



there is either a small tubercle or deep, open fossa. The septal formula is, however, seldom 

 complete or symmetrical. 



Large double calicles seem to be common. They are shallow and have a conspicuous, 

 nearly solid, columellar tangle, filling up the greater part of their bases. 



The colour of the unbleached stock is yellowish-brown. The axial strand is an open, 

 delicate, lamellate reticulum, round which the cortical layer is rather dense but mostly 

 conspicuously trabecular. 



The chief characteristics of this coral are its very variable wall-texture, its peculiar 

 granular surface, the large frosted granules being too coarse to give the surface a velvet-like 

 appearance. Tliey all appear separate tliough crowded, with here and there a smooth, delicate, 

 zigzag, sometimes even reticulate wall-thread developed between them. In certain regions 

 the granules thicken and become flaky, and then the calicles are hardly recognisable, and the 

 surface appears dense though rough and porous. The co-ordination of these surface granules 

 with the conspicuous trabecule seen in the section is obvious. 



These recent specimens are further interesting, because, although the central reticular 

 axis is fairly thick, it is not by any means so pronounced as it is in many of the Pleistocene 

 fragments described below (cf P. Barbados 6). In these latter the thin, cortical layer is 

 nearly solid and quite distinct from the developed trabecular layer seen in the above. 



The bleached fragment of this coral shows the hollowing out of its skeletal elements by a 

 boring alga. 



a. Three large stems in a box with many . ^ool. Dept. 99. 6. 26. 10 (part), 



smaller fragments. I 



14 Porites Barbados 4. (P- Barhatce quarta.) (PI. II. fig. 1 ; PI. IX. fig. 7.) 

 [Barbados, coll. Gregory ; British Museum.] 



Description. — The corallum rises into rounded, slightly flexuous stems, often flattened, 

 rather more than 1 cm. thick. The forking is at small angles, with a tendency to curve outwards 

 from one another, and at short distances apart (1 • 5 cm.). The two prongs are often of unequal 

 sizes, the smaller becoming aborted and remaining behind, the larger and thicker growing and 

 again dividing. The stock expands partly by the outward curving of the branchlets. The 

 living layer is 5-6 cm. deep. 



The calicles are very ill defined, from 1 to 1 • 5 mm. in diameter, slightly depressed as 

 irregular breaks in the surface. The wall is here a slight zigzag thread, there it consists of 

 elegant, continuous flakes with rounded pores ; it is mostly very incomplete, variable in 

 thickness and texture, and without definite arrangement of its component elements. The 

 septa are thin and irregular, but as the walls become more soUd and flaky, they may appear as 

 thick, irregular ridges running over the walls, but without symmetry and only occasionally 

 projecting far into the shallow calicular depressions. Immediately below this irregular margin, 

 the skeletal elements become so flaky as almost to suggest a film spreading through a dying 



