AND PHYSIOLOGY OF THE SPONGIAD^. 
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Suborder IV. Simple fistulo-fibrous skeletons. Cavity of the fibre simple, central, and 
continuous. 
Spongia jistulosa, Lamarck. 
The genus Yerongia was described by me in the Annals and Magazine of Natural 
History for May and December 1845. 
The same relative difierences exist between the fibrous structures of the suborders 
six and seven of the second order, Silicea, that we observe between those of the first and 
fourth suborders of the third order, Keratosa. 
Suborder V. Compound fistulo-fibrous skeletons. Central cavity of the fibre single and 
continuous, having secondary csecoid branches radiating from it at nearly right 
angles. AulisJcia, Bowerbank. 
This genus was described by me in the Annals and Magazine of Natural History for 
May and December 1845. 
Suborder VI. Eegular semi-areno-fibrous skeletons. Skeleton regularly areno-fibrous, 
having a well-defined central line of grains of extraneous matter within the fibres. 
Stematumenia, Bowerbank. 
In the sponges of this suborder the extraneous material is subordinate to the keratose 
fibre, in which it exists in the form of a central line of sand or other extraneous matters, 
constituting an axial line in the fibre surrounded by a thick coat of pure keratode. The 
axial line of sand is generally confined to the primary fibres of the skeleton, the secondary 
ones being usually without it. A portion of the commonest Bahama sponges of com- 
merce belong to this order. 
Suborder VII. Irregular and entirely areno-fibrous skeletons. Skeleton irregularly areno- 
fibrous, having the skeleton-fibre filled from the centre to the surface with grains of 
extraneous matter. 
Bysidea, Johnston. 
In the skeletons of the sponges of this suborder the keratode appears subordinate to 
the extraneous matter ; the fibres frequently appearing to consist almost entirely of sand. 
Yerongia, Bowerbank. 
On the Arrangement of the Genera. 
The genus Halichondria, as established by Fleming and adopted by Dr. Johnston, 
when applied to the arrangement of exotic as well as British species, embraces so wide 
a range as to afibrd little or no assistance in the determination of species. Under this 
designation every known sponge would be arranged having silex as the earthy basis of 
its skeleton, however varied their anatomical structure might be, excepting the few 
species contained in the genera Geodia, Tethea, and Spongilla. 
Dr. Johnston, in his ‘ History of British Sponges,’ has divided the British species into 
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