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 considtji-ably compressed, and 

 have frequently grains of sand and spicula imbedded 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 interlacement of elongated fibres with 

 little or no gelatinous substance intervening, as represented by 

 PI. XIV. fig. 1, and these are covered by others similarly dis- 

 posed with their axes in a different direction, the mass being 

 bound firmly together by other fibres running in tortuous direc- 

 tions so 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 PI. 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 Organic Tissues 

 in the Bony Structure of the Coralhdse,^^ published in the ^ Philo- 

 sophical Transactions of the Royal Society,^ part ii. 1844, p. 220, 

 pi. 17. figs. 3 and 4, and also to the mode of the production of the 

 primary vascular tissue in the new basement membrane of Solen 

 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. i. p. 144, and figured 

 in pi. 18. fig. 4. a and h. 



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 Spongiada in connexion with 



