Happon anp Durrpren—Some Actiniaria from Australia and other Districts. 163 
various degrees of contraction, thicker in upper part of column in the region of 
the sphincter muscle, containing minute branched cells. Endoderm generally 
half the thickness of the ectoderm. The basal muscle is well developed. 
Sphincter muscle (Pl. x., fig. 5)-—The sphincter muscle is well developed, 
and extends for a considerable distance. The cavities are not filled with muscle 
cells. Their character is seen in the figure. 
Tentacles.—The ectoderm of the tentacles is crowded with small oval nemato- 
eysts, which, in some places, perhaps owing to the folding of the ectoderm, appear 
as if arranged in a pinnate manner. ‘The nervous layer of the ectoderm is well 
marked, and the muscle is strongly developed. The endodermal muscle is 
extremely feebly developed. 
Disc.—The histology of the disc resembles that of the tentacles, but the 
ectoderm is thinner, and the endodermal muscle is well developed. 
sophagus.—Large and much folded, with appressed walls in section; 
ectoderm regular, not folded, with glandular cells, and long dark granular nemato- 
cysts. 
Mesenteries.-We have found it impossible to accurately determine the arrange- 
ment of the mesenteries; but we think that the mesenteries are not in multiples 
of six, and that certain of the mesenteries which would correspond with the 
second cycle of a hexamerous form are perfect. The single pair of directives, 
so far as we can make out, are sterile, and the other primary mesenteries are also 
probably so; the second cycle appear to be fertile ; the third cycle of mesenteries 
are imperfect and fertile; the fourth cycle are short and sterile. 
The mesogloea is thin; the character of the retractor muscles will be seen on 
reference to Pl. x., fig. 4. 
Acontia are abundant and crowded with very long nematocysts. 
Gonads.—The specimen examined was a female. 
Mitactis similis, n. sp. 
(Pl. vu, fig. 15.) 
Form.—Short, thick column; oral and pedal discs somewhat wider than 
column ; tentacles sub-equal, short, thick, blunt, in three or four cycles. 
Colour.—Uniform deep orange, almost a terra-cotta tint; tentacles paler, a 
sort of flesh-colour. 
Dimensions.—Height of column, about 16 mm.; diameter of oral disc, about 
16 mm.; length of tentacles, 2mm. ‘These figures are only very approximate. 
Locality —Port Philip. 
We have given this species its name from the fact that it appears to closely 
resemble the preceding species in its external characters. 
TRANS. ROY. DUB. SOC,, N.S. VOL. VI., PARI VI. 2C 
