78 DR.J.S. BOWERBANK ON SILICEO-FIBROUS SPONGES. [ Jan. 28, 
structure as well as from its external aspect, in the preceding manner. 
The type specimen was a widely expanded cup 163 inches in dia- 
meter. It was divided into about equal parts; one half remains in 
the Bristol Museum, and the other is in the British Museum ; the 
sides rather exceeded an inch in thickness. 
The expansile dermal system, which usually contains the most 
strikingly characteristic parts of such sponges, is entirely absext from 
the general mass of the animal. The nature of the dermal mem- 
brane, the pores, and the oscula are therefore unknown to us ; but 
without the aid of these organs there still remain sufficient perma- 
nent specific characters to enable us to readily separate this species 
from its nearly allied congeners, in their present denuded state. Of 
the two species in the British Museum, Dactylocalyx pumiceus and 
Iphiteon Ingalli, the latter has been figured by Dr. Gray in the 
‘ Proceedings’ of this Society for 1867 (plate 27. fig. 2), and has 
been erroneously designated Dactylocalyx pumicea; and this error 
is the more remarkable as the surface-characters of the two spe- 
cimens differ very materially from each other. The outer surface 
of D. pumiceus is furnished with deep channel-like depressions, dis- 
posed in irregular lines radiating from the basal portion towards the 
margin of the sponge. These channels or large interstitial spaces 
penetrate deeply into its substance, so as to convey within it the 
newly imbibed streams from the inhalant pores. On the upper 
surface of the sponge these channels do not exist ; but 7m iew of them 
there are numerous large round or oval orifices, varying in diameter 
from about two lines to nearly half an inch. There is a slight ten- 
dency to an arrangement in lines radiating from the centre to the cir- 
cumference. There can be little doubt of these orifices being the 
terminations of the great excurrent system of the sponge, and that 
above each of them in the living state there would be the true oscula 
of the dermal system of the sponge, JI. Ingalli differs materially in its 
surface-characters from D. pumiceus. The inner surface of the cup 
is furnished with numerous deep channels or depressions with sharp 
margins, while in D. pumiceus the corresponding part of the sponge 
is occupied with numerous circular or oval orifices with rounded 
margins; the outer surface of I. Ingalli is furnished with deep 
more or less sinuous channels with rounded margins, while the si- 
milar channels in D. pumiceus are decidedly arranged in nearly 
straight lines. Beside these differences in external appearance, the 
characters of their respective skeletons at once separate them not 
only as species, but as genera. The irregular structure of D. pu- 
miceus is readily to be distinguished from the characteristic symme- 
trical configuration of the circular confluent areas of [phiteon. 
There is alsa in the British Museum a piece of D. pumiceus, about 
2 inches long by 13 inch broad and about 3 inch thick, on a tablet, 
said to be from Barbadoes; this is probably a fragment off the large 
specimen from the Bristol collection, as its microscopical characters 
agree precisely with those of the large portions which I have exa- 
mined. 
There is also a small specimen of the species in the Belfast Mu- 
