1094 
DE. J. S. BOWEEBAKK ON THE ANATOMY 
formed sponges, we shall find in all cases that those organs exist only on the inner 
surface of the great cloacal cavities. 
The construction of the interstitial cells is best demonstrated in a longitudinal section 
of a dried specimen of Grantia ciliata, mounted in Canada balsam ; and in a specimen 
so prepared, spaces are seen between the cells, which are often nearly half the size of 
the cells. These spaces are most probably produced by the contraction of the tissues 
induced by the mode of the preparation of the object, and do not exist in the Ihing 
sponge ; but they serve admirably to demonstrate the fact that each interstitial cell has 
its own special parietes, and that the divisions between the cells are not common to 
adjacent cells. Plate LXXII. fig. 1, and (Part II.) Plate XXXIII. figs. 1 & 2. 
Leucosolenia, Bowerbank. 
Grantia, Fleming and Johnston. 
Sponge fistular, formed of a single layer of triradiate and other spicula surrounding 
a large central cloaca, which extends into all parts of the sponge. 
Type, Grantia botryoides, Fleming. 
The structure of Grantia hotryoides, Fleming, difiers essentially from that of Grantia 
compressa of that author, inasmuch as there is a total absence of the interstitial cells 
which are so characteristic of the latter sponge ; and its structure is equally discrepant 
when compared with that of Grantia nivea of Fleming ; for although it possesses cloacae 
in common with that species, it has no approximation whatever to the massive Hali- 
chondroid form of the substance of that sponge. On the contrary, its parietes con- 
sist of a single thin layer of spicula and membranous tissues surrounding a large central 
sinuous cloaca. Plate LXXII. fig. 2. 
Leuconia, Grant. 
Grantia, Fleming and Johnston. 
Sponge furnished with cloacae, one or more. Parietes of sponge formed of a mass of 
irregularly disposed interstitial membranes, and triradiate and other spicula; per- 
meated by sinuous excurrent canals, the oscula of which are UTegularly disposed 
over the surfaces of the cloacae. 
Type, Grantia nivea, Fleming. 
Grantia nivea of Dr. Fleming is very different in its structure from either G. compressa 
or ciliata, or of G. botfpoides of that author. It has not the regular interstitial struc- 
ture of either of the first two, nor the simple fistulose form of the latter one, but, with 
the exception of the form of the spicula, it closely simulates the structural character of 
the siliceous germs'. HalicJiondria, while it is allied with the before-named calcareous 
sponges by the possession of cloacae. In consequence of these marked differences in the 
structure of the skeleton, I have separated it from Grantia as defined by Dr. Fleming, 
and constituted it a genus, adopting the term Leuconia, which was proposed by Dr. Geant 
as a general designation of the whole tribe of calcareous sponges. Plate LXXII. fig. 3. 
