MOLLUSCA. 271 



even those of thick shelled, full-grown Mussels. When 

 dead, a vessel of cream-coloured matter may be found in 

 the body, under the veil of the tentacles. On opening the 

 mem.brane the matter exudes, and if spread upon linen 

 colours it yellow ; the yellow changes to pea-green, thence 

 after a time to grass-green; becoming bluish by degrees 

 till it is quite blue. A tinge of red next begins to ap- 

 pear, increasing until the general tint is purple. This 

 is one of the purple dyes, and has been used in com- 

 merce for the purpose of colouring linen. The name how- 

 ever was originally applied to a Mnrex. I have just seen 

 a specimen of this Mollusc living in one of Mr. Lloyd^s 

 tanks, covered entirely with small Balani, each throw- 

 ing out its network of cirrhi from between the opening 

 opercula. 



Saxicava rugosa 



Has the power of boring into rocks and enclosing 

 its body and bivalve shell, in the hole it has scooped out 

 for a dwelling. It lives near the surface, so as to pro- 

 trude its siphon, which appears like a crimson wart on 

 the face of the rock, Avithdrawing it instantly on being dis- 

 turbed. 



