182 BRITISH SPONGES: 



Plate XXI. Fig. 8. 



Spongia nivea, Grant in Edin. Phil. Journ. xiv. 339 ; and in Ediri. 



New Phil. Journ. i. 168; and ii. 139, pi. I, fig. 14—16, copied 



in Blainv. Actinol. pi. 94. 

 Grantia nivea, Flem. Brit. Anim. 525. 

 Calcispongia nivea, £/a«wy. Actinol. 531. 



Hub. On the under surface of sheltered rocks at Prestonpans 

 Bay, during the ebb of stream tides, Dr Grant. On the 

 Northumberland coast at Dunstanborough castle, Mr Robert 

 Embletun. At Scarborough, BIr Bean. 



Sponge incrusting, spreading irregularly to the extent of one 

 or two inches in diameter, from one to two lines thick, snow- 

 white, of a light close texture, the surface shortly villose, even 

 or unequally protuberant or crested and waved, the under side 

 imperfectly cellular ; fecal orifices scattered, small, round with 

 a plain margin and level with the surface : the whole sponge 

 composed of spicula irregularly compacted, the triradiate very 

 numerous and of various sizes, some being minute and others so 

 large as to be visible by the naked eye. " The second form of 

 spiculum in the S. nivea is the most remarkable, though the 

 rarest ; it consists of a straight line, with two opposite lateral 

 projections in its middle, which are generally a little curved. 

 When these lateral processes are large and straight, it becomes 

 a regular quadriradiate spiculum, but they are generally much 

 shorter than the other two rays ; and when they are placed 

 near one extremity of the spiculum, it appears under the micro- 

 scope like a small dagger with a handle. The quadi-iradiate spi- 

 cula are generally very minute, and in niunber about one to a 

 himdred of the triradiate. The third kind of spiculum in this 

 species is a very minute straight equally thick spiculum, obtuse 

 at both ends, and generally about the fiftieth of a line in length ; 

 this form is very abundant, and may possibly be derived from 

 the broken rays of very small triradiate spicula, as in the com- 



