12 THE ELEMENTS 



of two parts or valves, generally con- 

 nected by a cartilage ; for example, 

 the cockle and muscle. 



The third order, univalve, consists 

 of shells complete in one piece ; for 

 example, the periwinkle and whelk. 

 This order is subdivided : first, into 

 those with a regular spire, and those 

 without a spire. 



The first order consists of three 

 genera: Chiton, Lepas, and Pholas. 



The second order consists of twelve 

 genera: Mya, Solen,Tellina, Cardium, 

 Mactra, Donax, Venus, Spondylus, 

 Chama, Area, Ostrea, Anomia, My- 

 tilus, Pinna. 



The third order consists of nineteen 

 genera: Argonauta, Nautilus, Conus, 

 Cypraea, Bulla, Voluta, Buccinum, 

 Strombus, Murex, Trochus, Turbo, 

 Helix, Nerita, Haliotis, Patella, Den- 

 talium, Serpula, Teredo, and Sabella. 



It will now be proper before pro- 

 ceeding to a detail of the Linnean 



