Happon ann Durrpen—Some Actinaria from Australia and other Districts. 145 
It agrees with G. mutuki and G. isolata, and differs from G. Macmurrichi in 
having a continuous ectoderm, ¢@.e. not broken up by strands of mesoglea. It also 
differs from the latter, and agrees with the other three species in the presence of 
zooxanthelle, The musculature of the mesenteries is only slightly developed in 
G. Macmurrichi and G. mutuki, while it is fairly well developed in our species. 
It agrees with G. Macmurrichi in having only a weak tentacular ectodermal 
musculature. 
PALYTHOA, Lamouroux, 1816. 
Palythoa Gregorii, n. sp. 
(Pl. vu, fig. 3.) 
Form.—Ccenenchyme not distinguishable from the walls of the polyps; each 
projects above the general surface of the ccenenchyme, leaving irregular linear 
polygonal depressions between them. The projecting portion of each contracted 
polyp has the form of a flattened dome with a small central circular depression. 
No distinct capitular ridges and furrows. 
Colowr.—Sandy. 
Dimensions.—Average diameter of polyps,6 mm. The thickness of the colony 
is very variable, and with it the length of the polyps; greatest height, 27 mm.; 
least height, 10 mm. 
Locality —Mombassa, East Africa, collected by Dr. J. W. Gregory, of the 
British Museum. Only one colony incrusting an irregular base of nullipores. 
The species is named after its distinguished collector. 
Body-wall.—The ectoderm, where present, is continuous, of considerable thick- 
ness, and covered with a cuticle; large yellow oval nematocysts occur, which 
clearly show the internal spiral thread, as well as a large number of narrow 
elongated nematocysts. 
The mesogloea is not very abundant, and contains numerous isolated cells; 
cell-islets and lacunze of all sizes crowd the mesogloea, and contain large yellow 
nematocysts and zooxanthellae. The incrustations, which extend throughout the 
mesogloea, consist of fairly large quartz sand grains, a few sponge spicules, some- 
what more numerous in the retracted or distal portion of the polyps, and a very 
little calcareous matter. 
The endoderm is entirely macerated away, leaving only numerous zooxan- 
thellze. 
Sphincter muscle (Pl vun., fig. 7)—The sphincter muscle is single, mesoglceal, 
and of a considerable length. 
