332 Rev. T. Hincks’s Contributions towards a 
MacGillivray describes two species which he regards as 
new, C. ligulatum and OC. spicatum; but the differences 
between these forms and M. roborata must be regarded, I 
think, as merely varietal. The unilaminate condition of the 
zoarium has certainly no specific value ; cases are not rare in 
which the bilaminate structure and the unilaminate occur in 
one and the same species. The other points relied upon—the 
more slender branches, the occurrence of one avicularium 
instead of two, the slight differences in the spines, and the 
spike-like process on the ocecium—are all weil within the 
limits of specific variation *. 
Ibid. (p. 70 sep.). 
Membranipora amplectens, sp. n. 
This interesting form is entitled to rank as the type of a 
new genus on the ground of the remarkable structure of its 
ovicelligerous cells. The ocecium itself is not merely a varia- 
tion upon the ordinary form, but has a distinct morphological 
character. 
Family Membraniporide. 
HETEROGCIUM, gen. nov. 
Zoecia pyriform, aperture large, occupying about two thirds 
of the front, closed in by a membranous covering and fur- 
nished with marginal spines (calcareous) ; immediately below 
the aperture a tall articulated spine. Owctum borne on 
gigantic cells, which are elongate and of considerable width, 
extending over almost the whole of the aperture, which is 
covered by a roof composed of rib-like processes springing 
from the opposite sides of the cell-wall, and bending slightly 
inward so as to meet in the centre, where their extremities 
are soldered together, whilst they are united laterally by a 
calcareous expansion, the oral arch pointed; ovdcelligerous 
cells placed between the divergent lines of zocecia at a bifur- 
cation. 
This form is nearly allied, so far as the structure of the 
zocecium is concerned, to the group of Membraniporidee which 
Busk (following d’Orbigny) has referred to the family Elec- 
trinide f, but is separated from it and from all the Cheilo- 
* C. ligulatum and C. spicatum are placed amongst the synonyms of 
Membranipora roborata in Miss Jelly’s ‘ Catalogue,’ 
+ ‘Challenger’ Report, pt. 1, p. 77. 
