AND PHTSIOLO&T OF THE SPONGIAD^. 
1117 
Suborder V. Compound reticulate skeletons, having the primary reticulations fibro- 
spiculate, and the interstices filled with a secondary spiculo-reticulate skeleton. 
Di^lodemia. 
This genus forms a connecting structural link between the orders Silicea and Keratosa. 
The structure of the keratose fibre would indicate its place to be in the third suborder 
of the latter ; but the presence of the Halichondroid secondary skeleton in such force, in 
conjunction with the irregular spiculated structure of the keratose fibrous primary 
skeleton, has induced me to place it among the Silicea. For more minute information 
regarding its structural peculiarities, I must refer my readers to the following description 
of the generic characters of Bij^lodemia. 
Diplodemia, Bowerbank. 
Skeleton fibrous ; fibres keratose, hetero-spiculous ; combined with a secondary skeleton 
of irregular network of spicula ; rete unispiculate, rarely bispiculate. Ovaries mem- 
branous and spiculous. 
The fibres in the skeleton of the only known species in this genus are very remark- 
able. They are smooth and cylindrical, having an axial line of, generally speaking, 
single spicula united at their points, running throughout the whole length of the fibre. 
But when it is of more than ordinary diameter, there are frequently other spicula at 
intervals imbedded in the fibre, parallel to the axial series. Throughout the whole 
length of the fibres, at short intervals, there are similar spicula to the axial ones, 
imbedded at right angles to the axis of the fibre, frequently projecting from the surface 
for half, or more than half, their length. Some of these projecting spicula originate 
small lateral branches of the keratose skeleton ; hut by far the greater portion of them 
are the connecting points of the keratose fibres and -the reticulo-spiculate secondary 
skeleton, the former being thus completely imbedded amidst the latter. 
The structure of the ovaria in this genus is also peculiar to it. The wall is very thin, 
and appears to consist of a single membrane profusely furnished with spicula which 
cross each other in every dhection, and occasionally appear to assume a somewhat 
fasciculated arrangement. They are not uniform in shape, some being regularly oval, 
while others are more or less ovoid. 
But one species of this singular genus is known, J). vesicula, Bowerbank, MS., from 
deep water at Shetland. Plate LXXIIl. fig. 8, and Part II. Plate XXXIV. fig. I. 
Suborder VI. Solid siliceo-fibrous skeletons. Skeletons reticulate. Fibres composed 
of concentric layers of solid silex, without a central canal. Beticulations unsym- 
metrical. 
Dactylocalyx, Stutchbury {Iphiteon, French Museum). 
The structure and mode of growth in this suborder of siliceo-fibrous sponges appear 
