92 DR, J.S. BOWERBANK ON SILICEO-FIBROUS SPONGES. [Jan. 28, 
rounded. Oscula small, slightly elevated, dispersed, very numerous. 
Pores inconspicuous, dispersed. Expansile dermal system—dermal 
membrane abundantly spiculous. Connecting spicula furcated, at- 
tenuato-patento-ternate, large and numerous; heads combining to 
form an irregular dermal network. Retentive spicula elongo-at- 
tenuato-stellate ; radii long and slender, rather numerous. En- 
veloping membrane of rigid skeleton—retentive spicula same as 
those of the dermal membrane, rather numerous. Skeleton—areas 
of reticulation round or oval, nearly equable in size ; fibre smooth, 
but umbonated at intervals; umbones cylindrical, smooth, short ; 
apices very nearly flat. Gemmules membranous, smooth, sub- 
globular. 
Colour, in the dried state, nut-brown. 
Hab. Madeira (H. N. Mason, Esq.). 
Examined in the dried state. 
The form of this sponge is that of a broad, irregularly sinuous, fan- 
shaped plate about 5 or 6 lines in thickness ; it is 73 inches high, 
123 inches wide, and 37? inches from back to front. On the latter, or 
inhalant surface, at about the middle of its width, there are three 
sinuously fan-shaped plates given off, the largest one from about 
midway between the base and top of the sponge, and two smaller 
ones from near the base; the upper one has grown on a plane about 
parallel to that of the parent sponge, and its inhalant and exhalant 
surfaces aecord with those of that portion of the specimen. The two 
lower ones are projected from the large sponge at nearly right angles 
to its inhalant surface; and they have their inhalant surfaces on 
their upper sides, and their exhalant ones within the folds of their 
under ones. 
The sponge has evidently been sessile: there are no remains of an 
expanded base, but the attachment has apparently been near the 
middle of the basal portion of the specimen; and it appears to have 
grown on a somewhat elevated piece of rock, as both of the extreme 
ends of the sponge project below the apparent plane of attachment. 
It is evidently an old and well-matured specimen, as it has numerous 
parasites attached to its inhalant surface, among which are several 
specimens of Vermetus, and three of what is apparently Caryophyllia 
Smithii, two of which are full-grown, and one of them has numerous 
parasites on its external surface. 
The condition of the sponge is excellent: all its organs are evi- 
dently in the state they were when it was taken alive from the sea ; 
and it has apparently never undergone the deterioration of immersion 
in fresh water, as a quantity of salt remains in crystals on its surface. 
This specimen is therefore especially valuable as leading to a 
natural elucidation of the general characters of the singular and 
beautiful class of sponges to which it belongs. 
The oscula present no very striking characters ; the margins are 
slightly elevated and rounded ; many of them are completely closed, 
while others are only partially so ; and through the central orifice on 
these the enveloping membrane of the rigid skeleton, thickly studded 
