MOLLUSCA. 295 



repairs the fracture of its shell with a material having 

 the same chemical composition as the original shell, 

 and differing in mechanical properties only in being a 

 little more opake." 



Fifth. " The repairing material is laid on from with- 

 out the shell, as it should be according to the theory 

 of the function of the membranous arms as calcifying 

 organs/' 



The sixth, and perhaps the strongest fact is, that 

 some young Argonaut cephalopods, bred in confine- 

 ment, were noticed by Madame Power to have formed 

 their little shell in ten or twelve days after their exclu- 

 sion from the egg. 



THE SEA SNAIL. 



(Janthina Fragilis.) 



The Sea- or Violet-Snail is one of the many hydro- 

 static univalve shells which float upon the surface of 

 the ocean, giving beauty to its bosom and relieving the 

 monotony of a calm. It varies much in size. The 

 largest I have obtained is equal in magnitude to the 

 shell of our garden snail, (Helix hortensisj to which it 

 bears, also, a close resemblance in form. The upper 

 part of the shell (including the whirls) is white ; the 

 entire inferior surface delicate-blue or violet. When 

 recently removed from the water, it is covered with a 

 slippery membrane, or periostracum, and has a lively 

 tint which cannot be artificially preserved. A delicate 

 white and inflated membrane projects horizontally for- 

 wards from the aperture of the shell. It is about one 

 inch in length, of oblong form, and is puckered on its 

 surface, so as to resemble an assemblage of air-bubbles. 

 It is an aeriferous float, and may in some measure serve 

 the purpose of an operculum : but more questionably 



