110 IXTEODL'CTION TO COXCHOLOGY. 



claw, which becomes filled with calcareous matter, the 

 hinder one being tlirown over the siphon so as nearly to 

 conceal the primitive growth of the sliell from the ob- 

 server; the mantle then withdraws, and, subsiding in 

 wrinkles, deposits that richly-coloured layer of corresponding 

 enamel, with which the columella and the aperture are uni- 

 formly adorned at maturity. 



The distinguishing peculiarity of the Pterocera, or Spider- 

 shell, as regards liis testaceous covering, consists in a wing- 

 like expansion of the mature lip. This genus inhabits the 

 seas of the tropics. 



Stromli are generally distributed tlu'oughout the globe. 

 The largest species, S. gigas, is from the TTest Indies, and 

 several others abound in the same locality ; they are also 

 discovered in the seas of China, Ceylon, and the Moluccas, 

 with those of Austraha, Xew Zealand, Peru, California, the 

 Sandwich Islands, and the Red Sea. 



