GASTEROPODA. 279 



from twenty to thirty pounds have been given for a 

 good specimen. The shell is now far from rare, and 

 shillings take the place of pounds in the purchase. 



Fig. 2 16. -the wkntlk-tkap. 



The Violet Shells (Janthina), in their external 

 appearance, very much resemble our garden snails, 

 and are not furnished with an operculum. Instead 

 of this, however, they possess a very curious appara- 

 tus attached to their rudimentary foot, composed of 

 a substance resembling horny froth, that serves as a 

 float, whereby they are sustained at the surface of 

 the sea, and to which as to a raft the Janthina fastens 

 its eggs. These Mollusks are common in the Medi- 

 terranean : on touching them they emit a violet- 

 coloured fluid that dyes the water around them of a 

 deep purple colour. 



The Cone Shells (Comis) (Fig. 217) are remarkable 

 for their conical shape and the flatness of their spire, 

 as well as for the extraordinary beauty and brilliancy 

 of their colours. These shells, in Africa, in regions 

 far from the sea, are considered of as great value as 

 the Lord Mayor's badge is in London, and are so 

 highly prized as evidences of distinction, that for 

 two of them a slave may be bought, and five w^ould 

 be considered a handsome price for an elephant's 

 tusk worth ten pounds. 



The Cowrie Shells {Gyp-asa), many of which form 



