Haddon and Shackleton — Actinm : I. ZoantJiece. 685 



Our deeper water specimen was shorter and relatively much more tuberculated. 

 In the " Special volume of the Proceedings of the Geographical Society of 

 Australasia" (Sydney, 1885), under a section designated as "New Gruinea 

 Exploration," there is a letter from Dr. J. W. Haacke, concerning a collection of 

 Anthozoa fi'om Thui'sday Island, Torres Straits, in which he refers to " a species 

 belonging probably to a new genus closely allied to the genera Polythoa and 

 Zoanthus. This genus would be characterized by showing, even externally, a very 

 obvious bilateral symmetry, better, I believe, than any other An thozoou " (p. 225), 

 There is no doubt that this is our new species. 



We have copied Grray's account of the other Australian representative in our 

 account of the genus, the absence of tubercles readily distinguishes it from our 

 species. The same also holds good for the Port Natal species, I. spongiosa. 



Body-zvall (PI. Lxn., fig. 4). — The thick body- wall is covered by a cuticle as 

 in the species of Zoanthus described. The ectoderm is not continuous, but is 

 broken up into fairly uniform groups of cells by well developed strands of 

 mesogloea, which connect the peripheral with the general mesogloea (PI. lxiii., 

 fig. 6). Amongst the ordinary columnar cells of the ectoderm are to be found 

 numerous zooxanthellje, as well as occasional large nematocysts. Bays of 

 ectoderm, in which the cuticle may to a greater or less extent be involved, often 

 occur. Canals and lacunre of much smaller diameter than the anastomising canals 

 which occur in the species of Zoanthus we have described, are also present. Some 

 of these can be shown to be continuous with the ectoderm, whilst others have an 

 equally clear connexion with the endoderm (PI. lxiii., fig. 5). Endodermal baj's, 

 which may be quite shallow, or may extend to a greater or less extent into the 

 mesogloea as large open canals, are not unfrequent (PI. LXii., fig. 4; PI. lxiv., 

 fig. 9). Occasionally these are slightly branched. A few nematocysts, smaller 

 than those found in the ectoderm, as well as zooxanthellae, are present in the 

 endoderm. The endodermal muscular layer is well developed. 



Sjjhincter muscle. — The single mesogloeal sphincter muscle is extremely thick 

 and powerful. The cavities are well filled with muscle cells (PI. lxiii., fig. 4). 



Capitulum. — The cuticle and peripheral layer of mesogloea, as well as the 

 strands of mesogloea which break up the ectoderm, are present in that part of 

 the capitulum, which in contracted specimens is thrown into folds, but the cuticle 

 disappears, and the ectoderm becomes continuous as the tentacles are approached. 

 Disc and tentacles. — The usual small nematocysts are found in the outer part of 

 the ectoderm of the tentacles. The nuclei do not form a distinct central baud, but 

 are diffused, leaving, however, a clear band next to the muscle fibres. The 

 ectodermal muscular layer is remarkably well developed. The fibres are 

 supported on fine and complicated mesogloeal plaitings, forming in some cases a 

 band nearly equal to one-third of the entire thickness of the wall of the tentacle. 



