1872.] DR. J. S. BOWERBANK ON THE SPONGIADjE. 631 



able period. That which has apparently been its upper surface, 

 under these circumstances, is crowded with large irregularly shaped 

 depressed oscular areas, exceeding sixteen in number, and varying in 

 diameter from half an inch to an inch and half, the elevated ridges 

 intervening rarely exceeding a quarter of an inch in thickness, the 

 areas varying from one to six lines in depth. On that which has 

 apparently beeu the lower side of the sponge there are shallow indi- 

 cations of a few such areas ; hut the whole of this surface otherwise 

 is smooth and even compared with the upper one. The greater 

 portion of the surface is denuded of its large external defensive spi- 

 cula ; but on the under surface there is a triangular space ecpial to 

 somewhat more than a superficial square inch on which they are in 

 excellent preservation, intermingled with numerous spicula of the 

 secondary series of defensive spicula, all compressed and matted 

 together on the surface ; and in several of the oscular areas on the 

 upper surface the secondary series of external defensive spicula are 

 exceedingly numerous in situ and in their natural positions, and are 

 so abundant as to completely obscure those organs, like thick tufts 

 of wetted hairs. 



The oscula in each area are very numerous and closely adjoining 

 each other, and, as might therefore be expected, are very minute, 

 and are not visible until denuded of the secondary external defensive 

 spicula. 



The pores are dispersed over all parts of the sponge not occupied 

 by the oscular areas ; they are very minute, and are scarcely visible 

 with the aid of a lens of an inch focus. 



The dermal and interstitial membranes have hut few comparatively 

 of the fusiform tension-spicula, which are of the same form and of 

 about the same size as those of the external secondary series of 

 defensive spicula ; but both descriptions of membranes abouud with 

 the minute short fusiformi-cylindrical incipiently spined retentive 

 spicula. These organs are exceedingly interesting, and very cha- 

 racteristic of the species. They are irregular in their forms and 

 proportions ; but when well developed they are about three times 

 the length of their greatest diameter, and their length, as compared 

 with the diameter of a full-sized skeleton -spiculuin, is as about one 

 to eight. They are so minute as to require a microscopical power 

 of about 800 linear to define their form and spination distinctly. 

 In some parts of the membranes they are so numerous as to entirely 

 obscure the tissues beneath them. 



The attenuato-stellate retentive spicula of the interstitial mem- 

 branes are variable iu size, ranging in extreme diameter (from oppo- 

 site points of their radii) from one fourth to about one third of the 

 diameter of an adult skeleton-spiculum. The radii of the largei 

 ones are few in number and frequently incipiently spinous ; compa- 

 ratively speaking, they are not very numerous. The large fusiformi- 

 acerate spicula of the primary external defensive system are few in 

 number ; but, to compensate for their comparative scarcity, those of 

 the secondary system of defensive spicula are exceedingly numerous, 

 and especially so in the large shallow oscular areas. They are pro- 



