with descriptions of some new genera. 407 
sionally imbedded. Interstitial substance fibro-membranous. 
Investing membrane simple. 
S. scyphus. Sponge sessile ; when immature massive, when adult 
cup-shaped; surface coriaceous, spinous. Excurrent oscula 
large, usually dispersed over the interior of the cup. 
The fibres of the skeleton of the members of this genus are 
rigid when dry, but in a wet condition they possess a consider- 
able degree of elasticity. The smaller ones are nearly cylindrical, 
and are usually without either spicula or grains of sand; but the 
larger and more mature fibres are considerably compressed, and 
have frequently grains of sand and spicula cubed in the sub- 
stance of the horny structure. 
The most remarkable character in this tribe is the singular 
nature of the interstitial matter of the sponge, which is con- 
structed of a beautiful mterlacement of elongated fibres with 
httle or no gelatinous substance intervening, as represented by 
Pl. XIV. fig. 1, and these are covered by others similarly dis- 
posed with thew axes in a different direction, the mass being 
bound firmly together by other fibres running in tortuous direc- 
tions sc as to cement the whole into a membrane, as it were, of 
great strength and tenacity. Each fibre is of considerable length, 
but from their matted condition I have been unable to separate 
an unbroken one from the mass. They appear usually to have 
obtuse terminations without any attenuation towards the ends, 
but occasionally fibres are observed with large cytoblastic termi- 
nations, as represented by Pl. XIV. figs. 3 and 4. 
The origin of this description of tissue appears to be similar 
to that of the sacculated tissue of Cellepora pumicosa, which I 
have described and figured in a paper “On the Crganic Tissues 
in the Bony Structure of the Corallidee,” published in the ‘ Philo- 
sophical Transactions of the Royal Society, part 1. 1844, p. 220, 
pl. 17. figs. 3 and 4, and also to the mode of the production of the 
primary vascular tissue in the new basement membrane of So/en 
vagina, described in a paper “ On the Structure of the Shells of 
Molluscous and Conchiferous Animals,” in the ‘Transactions of 
the Microscopical Society of London,’ vol. 1. p. 144, and figured 
in pl. 18. fig. 4. a and 0. 
The fibres have usually a number of gelatinous-looking mole- 
cules, imbedded in the surface, which vary much in their size 
and form, as seen in Pl. XIV. fig. 5, which represents a portion 
of one of them examined by transmitted light with a linear power 
of 1020; and the cytoblastic terminations also are thickly studded 
with them, as represented in Pl. XIV. fig. 4. 
This description of fibrous tissue is the more remarkable when 
we view its occurrence among the Spongiade in connexion with 
