100 MADREPORARIA. 



forking seems to be rapid, 1 cm. apart, nearly all in the same plane, but frequently aborted, 

 leaving knee-bends or thin rounded processes. These latter may secondarily grow in length 

 and show one or more knee-bends, but they remain much thinner than the main continua- 

 tions of the stems, wliich keep fairly uuilbrm in thickness. The living layer in the single 

 slantingly grown specimen is 3 cm. deep. 



The calicles are variable in size, many 2 mm. and more in diameter, as concave, sub- 

 circular depressions. The walls are not high, but are conspicuous, thin and sharp-edged. The 

 wall-thread itself is frequently absent, but when developed, very closely zigzag. Where its 

 tlu«ad is not developed, the septa of adjacent calicles are arranged close together. Here and there 

 rows of two, three and more of these calicles run almost together, the intervening walls being 

 very faintly traceable. The septa appear as rather irregular rows of granules, diminishing 

 towards the centre ; wall granules, septal granules and pali, with a small central tubercle, can 

 be made out. But as the granules fuse irregularly together, they appear to vary in size and 

 the pali vary in number. The directives frequently appear short and apart from the walls, 

 owing to the breaking up of the edges of the septa. The central tubercle is sometimes 

 flattened in the directive plane. 



The section shows a great thickness of axial reticulum which forms the tips of the 

 terminals, surrounded by a thick, nearly solid, cortical, trabecular layer. 



The unbleached portion of the coral is a brownish-grey. 



This coral is unfortunately only a single specimen, which seems to have grown out 

 laterally at an angle of 40° to the horizon. We have no means of knowing whether this is 

 normal or accidental. The calicles are large, and somewhat peculiar among the West Indian 

 forms in having the septa as rows of minute frosted granules. All the rest of the characters, 

 however, point to its belonging to this region. The sudden contrast between the delicate 

 surface elements, and the great thickness of the elements seen in the section apparently right 

 up to the surface has been already noted, see P. Florida 3 and 5, P. Bermuda 1, etc. (see p. 143). 

 The axial reticulum is not only large and open, but shows in cross-sections the radial symmetry 

 of the calicles which developed in it. 



The specimen was labelled Porites clavaria, apparently because it somewhat resembles 

 that figured by Ellis and Solander.* The resemblance stops at the fact that both corals 

 consist of single forkings of stout stems, and is of absolutely no morphological importance. 



a. Zool. Dept. 1906. 1. 1. 9. 



89. Porites West Indies x. 24. {P. Americana incertw sedis quarta et vicesima.) 

 (PL VI. fig. 4; PI. XVII. fig. 10.) 



[British Museum.] 



Description. — The corallum shows a large, convex, encrusting base, 8 cm. in diameter, 

 without free edges, and rising to about 1 cm. thickness in the centre. The surface is perfectly 

 * Zooph., pi. xlvii. fig. I. See above, p, 81, for a description of this Porites. 



