. 1098 
DE. J. S. BOWEEBANK ON THE ANATOMY 
three sections, dependent on their form, a character so mutable among the Spongiadae, 
as to render it of little value, under any circumstances, when unaccompanied by struc- 
tural peculiarities. I have therefore thought it advisable to distribute the genera 
included in the order Silicea among seven suborders, founded on the most striking pecu- 
liarities of the structure of the skeleton. 
The first of these will consist of sponges having spiculo-radiate skeletons. Skeletons 
not reticulated, but composed of spicula radiating in fasciculi or separately from the 
base or axis of the sponge. This order will contain as many as fourteen distinct genera, 
the whole of which have skeletons the spicula of which are arranged in radial order. 
The mode of the radiation in these fourteen genera is not precisely the same, but they 
form three closely according groups, of which the leading genus of each of the fii’st 
two may be considered as the type. 
1. Geodia, Lamarck. 
2. Pachymatisma, Bowerbank. 
3. Edonemia, Bowerbank. 
4. Alcyoncellum, Quoy et Gaimard. 
5. Polymastia, Bowerbank. 
6. Halypkysema, Bowerbank. 
7. Ciocalypta, Bowerbank. 
The second group contains : 
1. Tetliea, Lamarck. 3. Pictyocylindrus, Bowerbank. 
2. Halicnemia, Bowerbank. 4. Phakellia, Bowerbank. 
In the whole of the first two groups, excepting Halyphysema, the skeleton-radiations 
are fasciculated to a greater or a less amount in the different genera. 
The third group will comprise : 
1. Microdona, Bowerbank. 
2. Hymeraphia, Bowerbank. 
3. Hymedesmia, Bowerbank. 
The most striking general character in these three genera is the extremely thin coat- 
ing-form of the sponge, and the radiation of the skeleton-spicula, either singly or in an 
irregularly fasciculated form, from a common basal membrane, the thickness of the 
sponge in some of the species being less than the length of one of the radiating skele- 
ton-spicula. 
Order II. SILICEA. 
Suborder I. Spiculo-radiate skeletons. Not reticulate. Composed of spicula radiating 
in fasciculi or separately from the base or axis of the sponge. 
Geodia, Lamarck. 
Skeleton : spicula fasciculated, radiating from the base or central axis of the sponge to the 
surface. Dermis crustular, furnished abundantly with closely packed ovaria. Ovaria 
siliceous, composed of cuneiform spicula, firmly cemented together by silex, in lines 
radiating from the centre of the ovary. Pores furnished with oesophageal tubes * 
* i. e. tubes resembling in tbeir office the oesophageal tubes of tlie higher animals. The expression 
^ pyloric valve ” used further on is to be understood in a similar sense. 
