with descriptions of some new genera. 409 
Haversian canals. In the sponge, these minute radiating canals 
are also present, but they are much fewer in number, and re- 
quire a power of 1000 linear to render them distinctly apparent. 
Under these circumstances they are seen, as represented in PI. 
XIV. fig. 6, radiating from the oat-shaped cavities, and usually 
decreasing in diameter until they terminate at unequal distances 
from the parent cavity, in exceedingly minute points. In many 
cases, the commencement of these mimute canals is expanded in 
the form of a funnel, so as beneath a power of about 500 linear 
to cause the oat-shaped cavities to appear fringed with a series 
of projecting points. 
The surface of the fibre is covered with nucleated cytoblasts 
and tessellated cellular structure in various stages of development, 
and in the centre of some of the more fully-developed of these 
cells, in place of their being entirely filled up by the secretion of 
cartilaginous matter, there is frequently an elongated cavity re- 
maining, which probably becomes one of these peculiar organs, 
after having been immersed in the cartilaginous substance of the 
fibre by successive layers of cellular structure. Occasionally, but 
by no means frequently, there are small patches of ramifying ca- 
nals situated immediately beneath the surface of the fibre, as re- 
presented at Pl. XIV. fig. 7 a, as seen with a linear power of 100. 
It is difficult to imagine what office these canals perform in the 
ceconomy of the animal, as they do not appear with the same de- 
gree of constancy or regularity as in other sponges where similar 
tissues occur in like situations. 
In some of the expanded portions of the fibre, there are often 
small round or oval holes, and around these the oat-shaped cavi- 
ties are arranged in a series of concentric rings, exactly repre- 
senting the mode of arrangement of the corresponding organs in 
true bone, in the vicinity of the Haversian canals. 
It is much to be regretted that there are no remains whatever 
of spicula or of fleshy interstitial substance to be found in this 
interesting specimen, nor am I aware of the part of the world of 
which it is a native, as it was procured from a dealer in natural 
curiosities, who could afford no clue to its previous history. The 
specific characters, therefore, must be considered as provisionally 
given, until other specimens may be found from which fuller and 
better characters may be established. 
The form of the sponge is that of a thick disc, the diameter 
being five and a quarter inches, and the thickness, one inch and 
three quarters. The two broad surfaces correspond exactly in 
form and structure; a portion of one of them is represented by 
Pl. XIV. fig. 8. 
There is no appearance, at any part of the sponge, of a point 
of attachment or base. 
Ann, & Mag. N. Hist. Vol. xvi. 2G 
