224 INTRODUCTION TO CONCHOLOGY. 



dinary mollusks, I have been induced to remember that 

 the same Almighty Being, who enables the Patella to re- 

 main unmoved in his conically-shaped dwelling amid the 

 fury of contending elements, who permits the feeble Chiton 

 to fold himself in a coat of mail resembling a perforated 

 pebble, and thus escape the notice of his marine enemies, 

 has determined the bounds of our different habitations, and 

 assigned to every incHvidual being his respective sphere of 

 action ; and that happy will it be for us, if we as steadily 

 perform our portion of allotted duty, as these feeble crea- 

 tures fulfil the purposes for which they are designed, in 

 accordance with their respective instincts. 



CJiUonelli may resemble their relatives the Chitons in 

 their general organization, but as regards the mantle, and 

 the structure of the shell, they differ materially. 



The mantle is thick and fleshy, peculiarly elongated, 

 sometimes covered with a harsh down, but in general 

 tough and leathery, and invariably destitute of any horny 

 cartilaginous part, or spines or bristles, or calcareous ar- 

 mature. 



Their valves, unlike those of the Chitons, which are 

 firmly set on a strong marginal cartilage, fitting and moving 

 one upon the other, like plate-armour, are of an oblong 



