220) MADREPORARIA. 
MAURITIUS. 
227. Porites Mauritius 51. (P. Mauritiensis prima.) (Pl. XXXII. fig. 6.) 
[Mauritius ; British Museum. ] 
Description.—The corallum forms a small, thin, slightly wavy or crumpled disc, uniformly 
about 2 mm. thick, and attached by its centre. The sharp edges are 1 mm. thick, supported 
by a thick, chalky epitheca, and expand horizontally and freely. 
The calicles are small, under 1 mm. across, ill-defined, with obscured radial symmetry. 
The walls are thick, slightly raised and rounded, apparently consisting of large coarse granules 
distinct and scattered. There is an irregular, incomplete ring of septal granules, similar to the 
wall granules, and often confused with them and with the irregular pali. These last are 
conspicuous to the naked eye, but excepting the four principals, are very irregular under the 
pocket lens. The fossa is small and mostly deep, with an occasional ill-defined central tubercle. 
The section shows a fairly regular reticulum with large round pores, in which the 
trabecule are only slightly more conspicuous than the horizontal elements. The colour of the 
unbleached corallum is nearly black. 
This Porites is so thin that when held up to the light the bleached parts are translucent. 
The single specimen is 5-6 cm. in diameter, and is associated with an explanate Montipora not 
unlike that called in Vol. III. p. 80, “ MZ. bilaminata.” 
a. Zool. Dept. 88. 10. 25. 22. 
228. Porites Mauritius 2. (P. Mauritiensis secunda.) 
[Mauritius ; British Museum. ] 
Description —The corallum is a fragment of a thick, massive block of unknown shape. 
The calicles are polygonal, the largest about 1:2 mm., and as shallow pits. The walls are 
very sharply ridged; they may be simple and thin or else reticular, but in the latter case the 
ridge persists, and the reticulum is added in the regular manner by the formation of inner 
synapticular walls; the synapticule are often so large that the inner wall is little more than a 
smooth, flat shelf running round the calicle. The septa run from the wall ridge over the shelf. 
They are thin and finely frosted or echinulate, and frequently unite with a large oval columellar 
ring at different depths below the surface. The pali in full formula are very inconspicuous as 
a large loose scattered ring. There is usually a flattened central tubercle in the large oval 
fossa; a large conspicuous columellar tangle can be seen. 
The section shows a regular trabecular arrangement, with large, numerous and irregular 
pores ; continuous horizontal elements can nowhere be seen. The colour is a rich buff, and 
penetrates 3-5 mm. below the surface in the section. 
