776 
BE, J. S. BOWEEBANX OX THE AXATOj\IT 
In Hyalonema mirahilis, Gray, a sponge nearly related to the genus AlcymceUum^ 
Quot et Gaimaed, we find another extraordinary series of internal defences ; one portion 
of the spicula appearing to be destined to wound and lacerate, rather than to retain 
intruding enemies, while a larger and stronger series of spicular weapons bear all the 
evidences of being to retain rather than to repel the assailants. 
. The first description of spiculum I have designated entirely spined, spiculated cruci- 
form spicula. They consist of a short stout cruciform base with a long spicular ray, 
ascendingly and entirely spinous, projected at right angles from the centre of the basal 
radii. The spines are acutely conical, and very sharply pointed. They pass off from the 
spicular ray at an angle of 12 or 15 degrees in the direction of its apex. The apices of 
the basal radii are attenuated and slightly spined. These spicula are thickly distributed 
on the fasciculi of the skeleton, and frequently equally so on one side of the interstitial 
membranes, probably that which forms the surfaces of the interstitial spaces, and they 
are especially abundant near the exterior of the sponge. The four basal radii appear 
firmly cemented to the membrane, but not immersed in its substance, as they do not 
appear to leave their impressions when removed from it, nor do they bring any portion 
of the membrane away with them. In some parts of the tissue these spicula are very 
much modified in form. In the ordinary cases we find the basal radii short and stout, 
and not more than a fourth or a fifth of the length of the spicular ray, while in other 
cases the basal rays are very nearly as long as the spicular one ; the only difference in 
their structure being that the latter is very strongly spinous, while the former have the 
spines comparatively very slightly produced. 
The second form is a large fimbriated multihamate birotulate spiculum, which occm’s 
dispersed amid the interstitial tissues of the large basal mass of the sponge. There are 
usually not more, than one or two together, but occasionally they occur in groups of ten 
or twelve, without any approach to definite arrangement. 
These spicula are comparatively large and stout. They have eight rays at each end of 
the shaft ; the two groups of radii curving towards each other to such an extent that each 
the perfectly blunt and cylindrical state of the arch of the hook bespeaks the design of retention as well as 
of destruction. As soon as the hook has penetrated to the inner blunt sur&ce of the curve, it no longer cuts, 
and the prey, wounded in every direction, is securely retained for the nutrition of the sponge. This result is 
indicated not only by the form of the spicula ; their position in the structure of the sponge bespeaks their 
office equally unmistakeably. They are not immersed in the sareode like their congeners in form, but are 
firmly cemented by one hook to the reticulating lines of the skeleton, while the other ends are projected at 
various angles into the interstitial cavities of the sponge in such numbers and in such a manner, that it 
would be next to impossible for an intruder within the sponge to escape being entangled and destroyed 
amongst them. Eig. 1, Plate XXXI. represents a portion of the reticulated skeleton of the sponge with the 
trenchant contort bihamate spicula in situ, magnified 50 linear ; and fig. 2 one of the spicula, magnified 400 
linear, to exhibit the trenchant edges and the cylindrical portions of the h/uni and shaft. 
This sponge is allied to Haliciiondria by the structure of the skeleton, and it is described by my friend 
Mr. J. Yate Johusox as being a thin coating species, spreading over the surface of rocks and stones to the 
extent of two or three inches in diameter. 
