ie 
608 DR. J. S. BOWERBANK ON ALCYONCELLUM [ Nov. 16, 
which they are immersed. Their complete immersion in the sarcode 
immediately beneath the dermal membrane indicates in a very satis- 
factory manner their peculiar office as expansile portions of the 
dermal system, and as organs of defence for the preservation of that 
important portion of the structure of the sponge. : 
The specimen of Hyalonema mirabile is in a much finer state of 
preservation than any of those which I formerly examined, and de- 
scribed in the ‘ Proceedings’ of this Society for 1867; and it has 
enabled me to complete the description of many parts of this extra- 
ordinary species of sponge, which the dilapitated condition of the 
specimens to which I then had access prevented me from determining 
with accuracy. 
The total height of the specimen received from the ‘Challenger ’ 
is sixteen and a half inches. The basal spongeous portion is of a 
conical form, two inches in height ; and the average diameter of the 
base of the cone is two and a half inches. It is a fortunate cir- 
cumstance that the basal membrane and that of the upper or conical 
portion of the spongeous mass are both in a perfect state of preser- 
vation. The basal portion of attachment is very sinuous and irregular, 
as if it had been adherent to an undulating surface which had been 
of somewhat soft consistence, so that it had been, separated from it 
without the destruction of the basal membrane of the sponge. The 
apex of the spongeous mass closely embraces the spiral column of the 
cloacal system ; and the lower part of the spiral column is completely 
buried in the basal sponge. The corium, in a more or less perfect 
state, extends from the apex of the spongeous cone for about seven 
inches of the remaining portion of the spiral column of spicula ; the 
remainder of which is bare, but spirally twisted to very near its distal 
termination. The corium is studded with the usual mamilloid 
oscular organs; and none of them exhibited the slightest indication 
of polypiferous contents, which we should naturally have expected 
to find, had such parasitical creatures been present, in a_ living 
specimen fresh from the sea, as the one in course of description evi- 
dently was. 
The adherent basal surface of the sponge has a distinctly marked 
boundary-line, consisting of a well-produced slightly compressed 
projecting ridge of membrane; and a difference of the structure of 
the basal and the upper portion of the dermal membrane is distinctly 
visible to the unassisted eye. This difference in their aspects arises 
from modifications in the reticular structures of the two parts to fit 
them for their respective offices. 
When small portions of each of the parts of the membrane were 
mounted in Canada balsam, their differences in structure became 
strikingly evident. The same forms of spicula were toa greater or a 
less extent present in both, but the modes of their distribution and 
arrangement were very different. The rete of the basal portion is 
comparatively compact and strong, and closely approaching regularity. 
It is constructed with the long inflato-acerate spicula which are com- 
mon to both parts of the membranous skeleton structure, but with a 
considerable mixture of large rectangulate sexradiate spicula, which 
