164 Happon anp Durrpen—Some Actiniaria from Australia and other Districts. 
Body-wall——Kctoderm fairly thick, with a distinct cuticle; dark-coloured, 
granular nematocysts in upper part of the column; basal muscle weak. Mesogloea 
thick, with numerous, very small branched cells, which give it a rather granular 
appearance. Endodermal muscle rather thick, and rising into a small ridge 
between the bases of the mesenteries. 
Sphincter muscle (Pl. x., fig. 5).—The single elongated mesoglceal sphincter 
muscle lies towards the centripetal or endodermal aspect of the mesoglea; the 
cavities are numerous and irregular, and their muscular lining is very thin. 
The muscles terminate inferiorly in very narrow, elongated spaces, which even- 
tually merge into the muscular layer of the endoderm. 
Tentacles.—The histology of the tentacles closely resembles that of the body- 
wall, but the mesogloea is not so thick. The dark-coloured nematocysts are more 
numerous, and the ectoderm is also crowded with small colourless ones. The 
ectodermal and endodermal muscles are well developed. 
Gsophagus.—The ectoderm of the cesophagus is thrown into deep folds, in 
which the mesogloea is implicated. There is no cesophageal groove. 
Mesenteries.—There are thirteen pairs of perfect mesenteries, two of which are 
directives; but these are irregularly disposed, as in the following formula :— 
13 (D.7. D. 4.) + 138 + 26=52. The mesogloea is very thick, and the plaitings 
of the retractor muscles are moderately complex. (PI. x., fig. 6). 
Externally this species is very like the last, at least judging from the sketches 
made by Professor Spencer. We think, however, that some of the anatomical 
details mentioned by us are sufficiently different to warrant us in regarding them 
as distinct species. We might recall the differences in the sphincter muscle, the 
more complex character of the retractor muscles of the mesenteries, and the 
thicker mesogloea in M. similis as compared with M. Australie. 
