198 J. E. DurRpEN—Jamaican Actiniaria: 
circular, light-coloured discs, or low mammiform prominences, distributed with 
considerable regularity over the surface of massive, dark-coloured sponges. What 
may be regarded as a very narrow border of ccenenchyme surrounds each indivi- 
dual polyp. Only occasionally are two or more polyps still united as a result of 
reproduction by budding, and all stages in the separation of one from the other 
can be observed. A thin ccenenchyme connects two polyps before their isolation, 
but chain-like colonies are never produced, as in the next species. The column- 
wall is smooth, but with a lens, minute, white, incrusting granulations are seen. 
These give a certain rigidity to the polyps, so much so that, in preserved material, 
the walls readily split in two. 
Retraction is complete in most examples; only a very small circular depression 
remains above, not sufficiently large to allow the mouth or dise to be seen. The 
capitular ridges are wedge-shaped, and number from twelve to sixteen, twelve 
bemg the most usual. The tentacles are extremely short, and, as seen in 
sections, are almost invariably twenty-four, arranged in two cycles. ‘The disc is 
circular and semi-transparent, and exhibits radiating grooves corresponding with 
the internal attachment of the mesenteries. The peristome is raised, the mouth 
slit-like. 
The ccenenchyme and column are dull white, due to the numerous included 
calcareous sand-grains; the tentacles and dise are dark brown. 
The diameter of retracted polyps is about 2°5 mm., the height 1°56 mm. 
ANATOMY AND HISTOLOGY. 
All that portion of the wall of the polyp which is embedded in the sponge may 
be regarded as the base, and discloses a different histological character from that 
of the free column-wall. It is convex in outline, but somewhat flattened and 
expanding peripherally, and is sharply marked off from the surrounding sponge 
tissue, showing that there is no intimate cellular relationship between the two. A 
very thin cuticle can also be traced (Pl. xiv., fig. 4). 
The ectoderm in places is not readily distinguishable from the mesoglea, the 
latter layer being so crowded with cells as to render the ground substance almost 
unrecognizable (Pl. xu., fig. 8). The ectodermal cells are large and more or 
less spherical in outline, not forming a columnar epithelium; their protoplasm 
stains very strongly. 
The mesogloea is broad, and, as a whole, stains very deeply, the result of the 
presence of the cellular constituents, mostly in the form of cell-islets. Cells 
are included to an extent greater than I have met with in any other Actinian ; 
they are all large, and the cytoplasm, in addition to the nucleus, readily takes up 
