CASSIDES. 101 



Would sound, and bid my bosom scom 

 The world's vain joys. 



" Its treasured idols all resigu, 

 That when life's cheating hues decline, 

 The one undying thought be mine, 

 To praise the Lord !" 



Cassides, or Helmets, are a strong, muscular, but inactive 

 group of moUusks, of wliich the sliells are chiefly distin- 

 guished by a solid or inflated growth and short spire, and 

 by the abrupt ascending recurvatui'e of the canal, through 

 which the siphon for conveying w^ater to the breathing- 

 organ passes, and which is of more than ordinary dimensions. 

 The faculties for building in this genus are somewhat 

 vigorously exercised : the mantle which lines the interior 

 of the shell extends in ample folds about the aperture, 

 and secretes that rich display of enamel, which afl'ords so 

 beautiful a material for the engraving of cameos. The 

 C. tubewsa, from the West Indies, is chiefly selected for 

 this purpose, on account of its delicate purity of colour. 

 The well-known Buirs-mouth, C. nc/a, offers a famihar 

 example of the great power exhibited by the genus in the 

 formation of shell, but, on account of its blood-red colour, 

 the enamel is not so well adapted for gem engraving. 



