6 Rev. T. Hincks’s Contributions towards 
connected with its neighbours by six stout but very short 
processes, which originate one at each extremity of the cell 
and two on each side. ‘These six connecting-bands are sepa- 
rated by as many rather deep depressions or hollows, which 
do not, however, pass through the zoarium. ‘The disconnec- 
tion of the cells therefore is only partial; but we have in this 
structure a most interesting transition-form between the solid 
and compact zoarium and the disjunct and retiform condition, 
which distinguishes the genus Diachoris. 'The dorsal surface 
of the zocecium in MM, radicifera is decidedly convex, and 
always bears a number of small raised tubular processes, from 
which the radical tubes originate. The latter are very slender 
and often of great length. 
The avicularium of this species is of a very interesting type. 
Though perfectly sessile and fixed, it is to a large extent of 
the bird’s-head form, and represents a developmental stage 
which is not far distant from the highest or articulated grade. 
In M. Carteri (see ‘ Annals’ for July 1880, pl. x1. fig. 8), 
which has a movable avicularium, we have a link between 
Membranipora and Bugula; through the present species the 
former genus is connected with Dzachoris, which has the 
closest affinity with Bugula. Wescem here to catch a glimpse 
of the lines along which the evolution of the Bicellarian forms 
may have proceeded. 
Membranipora inornata, un. sp. 
(Pl. IV. fig. 5.) 
Zoecia quincuncial, shallow, obscurely six-sided, often 
rounded at the top and bottom; margins thin, smooth ; aper- 
ture occupying the whole of the front, with a membranous 
covering, which lies on a level with the rim of the cell; 
orifice placed at the very top of the aperture in a kind of 
recess in the margin, much broader than high (almost trans- 
versely elliptical), the margin rising a little above it, and 
very slightly hollowed out to receive it. Ocwciwm(?). Zoa- 
rium flat, depressed, of a brownish colour. 
Loc. Bass’s Straits, on shell. 
This species bears a very close resemblance in many points 
to M. hexagona, Busk ; but a comparison of it with a British 
specimen of the latter (for which I am indebted to Mr. Busk’s 
kindness) shows them to be distinct. The cells of IZ. enornata 
are much larger than those of M. hexagona, and much less 
recularly hexagonal; the orifice is much larger and of a 
different shape, that of the British species being small, almost 
semicircular, and placed at some little distance from the top. 
