AND PHTSIOLOaY OF THE SPONGIAD^. 
825 
Fig. 6. A small portion of the kerato-fibrous skeleton of an Australian sponge, showing 
the attenuato-acuate entirely spined internal defensive spicula in situ dispersed 
on the skeleton-fibre, xl08 linear: page 773. 
Fig. 7. Verticillately spined internal defensive spicula dispersed on keratose fibres of the 
skeleton, from a West Indian sponge, Xl75 linear: page 773. 
Fig. 8. Verticillately spined internal defensive spicula from a keratose sponge from the 
West Indies. Congregated in fasciculi, X 175 linear: page 773. 
Fig. 9. A small portion of Hymeniacidon Cliftoni, Bowerbank, MS., exhibiting the 
membranous tissues of the sponge enveloping the fibres of a Fucus ; the 
defensive spicula over the fibre being erect, while those on the adjoining 
membrane are recumbent, Xl08 linear: — a, one of the attenuato-cylindrical 
internal defensive spicula, X 260 linear ; b, a small portion of the surface of 
the Fucus showing its cellular structure, x400 linear: page 774. 
Fig. 10. A portion of the reticulated skeleton of the sponge, with the radiating fasciculi 
of spinulo-quaternate internal defensive spicula in situ, X 108 linear : 
page 775. 
PLATE XXXI. 
Fig. 1. A portion of the reticulated skeleton of a sponge from Madeira, the fibres armed 
with trenchant contort bihamate spicula, x50 linear: page 776. 
Fig. 2. One of the trenchant contort bihamate spicula, showing the cylindrical form at 
the curves of the hook and the middle of the shaft, and the trenchant edges 
of the rest of the inner surfaces of the spiculum, x400 linear: page 776. 
Fig. 3. A portion of the skeleton of Hyalonema mirabilis, Gray, showing the mode of 
disposition of the multihamate birotulate and spiculated cruciform spicula in 
the body of the sponge. In the collection at the British Museum, X 50 linear : 
page 777. 
Fig. 4. A multihamate birotulate spiculum, magnified 175 linear, to exhibit the pecu- 
liaiities of its structure: page 777. 
Fig. 5. A spiculated cruciform spiculum, to show the relative proportions of the two 
forms of defensive spicula, Xl75 linear: page 777. 
Fig. 6. The same form of spiculum as fig. 5, showing the peculiarities of its spination, 
X 260 linear: page 777. 
Fig. 7. A small portion of the skeleton of Hyalonema mirabilis % Gray, from a speci- 
men in the Bristol Museum, showing the reticulations of the skeleton to be 
abundantly supplied, in some parts, with a small variety of multihamate biro- 
tulate spicula : a, one of the large spicula, of the same form as those in fig. 5, 
in situ, X 108 linear: page 777. 
Fig. 8 represents a small portion of the inner surface of the dermal membrane of Hyme- 
desmia Zetlandica, Bowerbank, MS., showing the fasciculation of the simple 
bihamate spicula, the equi-anchorate ones dispersed singly on the membrane. 
