142 Happon anp Durrpen—Some Actiniaria from Australia and other Districts. 
Mesenteries.—The arrangement of the mesenteries is brachyenemic. They are 
straight, and, owing to their number and well developed endoderm, almost fill 
up the cclenteron. The mesoglea is very thin, except parietally where it 
surrounds the large basal canal. These are mostly circular in transverse section 
(Pl. vur., fig. 3) except in the upper part, where they become ellipsoidal. The 
canal is filled with a deeply staining tissue. These basal canals are in communi- 
cation with the mesogloeal canals in the lower part of the column. In longitudinal 
sections they can be traced from near the base along the greater part of the 
length of the column. 
The musculature is weak, the mesogloea being only slightly plaited. 
Gonads.—Female gonads are developed in many of the specimens, They 
occur in the mesenteries at the upper third of the contracted column. 
Zoanthus Shackletoni has an external resemblance to Z. sociatus (Ellis), which 
has been minutely described and figured by M*Murrich (1889). This latter 
species is very common from the West Indies. We have communicated with our 
friend Prof. M°Murrich, and sent him specimens of our species. He informs 
us that its size is only about one-third of that of Z. sociatus ; that the sphincter 
muscle is entirely different in the two forms, since, in Z. sociatus, the proximal 
sphincter is relatively very much longer than in our species, and the outlines of 
the compartments of the lower part of these muscles is also very different. The 
basal canals are elongated in section in Z, sociatus, as shown in M*Murrich’s 
figure, but rounded in ours. As before mentioned, the remarkable appearance of 
the peripheral part of the body-wall may be due to unequal contraction, but this 
need not prevent it from forming an additional diagnostic feature, and so far as 
we are aware it is unique. 
Our species can also be readily distinguished from other described species of 
Zoanthus (ef. Trans. R.D.8., iv., 1891, p. 629). Amongst other characters, it 
differs from the more recently described Zoanthus chierchie, Heider, in its form, 
and in the character of its sphincter muscle, ectoderm, and cuticle. 
GEMMARIA, Duchassaing & Michelotti, 1860. 
Brachyenemic Zoanthez, with a single mesogleal sphincter muscle. Solitary, 
or connected by ccenosare. The body-wall is incrusted. The ectoderm is usually 
discontinuous, but may be continuous. Lacunz and cell-islets are found in the 
mesoglea. Dicecious. 
This definition of the genus differs only from that given in the Report of the 
Zoanthee from Torres Straits (1891), in the fact that the polyps may be connected 
by coenosare. M°Murrich (1889) considered that, in Gemmaria isolata, the polyps 
