162 Happon anp DurrpEN— Some Actiniaria from Australia and other Distriets. 
Sphincter muscle (Pl. x., fig. 1).—The character of the mesoglceal muscle is 
best understood from the figure. ‘The narrow elongated muscle-cavities are very 
characteristic, and give a striped appearance to the sphincter, which is more 
apparent in its lower half. It must be borne in mind that, at present, we are 
unable to say what variation in the appearance of sections of sphincter muscles 
may be attributed to different stages of contraction. 
Mesenteries.—There are twelve pairs of perfect mesenteries, of which one pair 
are directives. The mesenterial formula is 6 + 6 + 12 + 24, the fourth cycle 
being rudimentary. The first, second, and third cycles are fertile (ova in this 
ease). The character of the simple retractor muscles is shown in the figure 
(Pesci. 22): 
MITACTIS, n. g. 
Sagartians with a strong mesogloeal sphincter. A variable number, probably 
always more than six, of perfect mesenteries. One or two pairs of directive 
mesenteries. Body-wall without a membranous covering. Dise of not much 
greater diameter than the column. Tentacles short, conical in three or four 
cycles. 
Future investigations will show whether we are justified in erecting this new 
genus; at present we think it desirable to separate these forms from other 
Sagartians. We have named the genus from pizos, a thread, in reference 
to the acontia. 
Mitactis Australie, n. sp. 
(Pl. vu., fig. 14.) 
Form.—-Short, thick column, the height of which is about equal to the 
diameter of the oral and pedal discs, but it is somewhat narrower than them, 
evidently smooth and soft, and variable in shape. Tentacles sub-equal, short, 
thick, pointed, apparently tri-cyclic. Mouth small, rounded. 
Colour.—Uniform translucent buff; tentacles more of an orange colour; 
insertions of mesenteries show as light lines; ovaries shine through the body-wall 
as orange-coloured masses. 
Dimensions.—Height of column, 10 mm.; diameter of oral disc, 12 mm.; 
of column, 8 mm.; length of tentacles, 2mm. These figures are reckoned from 
the coloured drawing, and we cannot guarantee their absolute accuracy. 
Locality.—Port Philip. 
Body-wall._—EKctoderm regular, with a well-defined cuticle, a nucleated basal 
layer, and a fine ectodermal basal muscle. Nematocysts are very numerous, some 
being elongated and darkly granular. Mesoglea variable in thickness, owing to 
