EXPLANATION OF THE PARTS OF SHELLS. 15 



the denticulated lip being the last part of the shell which the 

 animal foims. The Strombus genus wants the expanded lip in 

 the young shell, from which circumstance it is frequently taken 

 for a species of the Buccinum and Murex. 



The Linnean arrangement of shells consists of three orders, 

 viz. MuUivalve, Bivalve, and Univalve. 



The first order, MuUivalve, is made up of shells consisting of 

 more parts than two. Every part of a shell which is connected 

 by a cartilage, ligament, hinge, or tooth, is called a valve of such 

 shell. 



The second order, Bivalve, is made up of shells having two 

 parts or valves, generally connected by a cartilage ; for example, 

 the Cockle and Muscle. 



The third order, Univalve, is made up of shells complete in 

 one piece ; for example, the Periwinkle and the Whelk. This 

 order is sub-divided : first, into shells with a regular spire, and 

 those without a spire. 



The first order consists of three genera : Chiton, Lepas, and 

 Pholas. 



The second order contains fourteen genera : Mya, Soleii, Tel- 

 lina, Cardium, Mactra, Donax, Venus, Spondylus, Chama, 

 Area, Ostrea, Anomia, JMytilus, Pinna. 



In the third order there are nineteen genera : Argonauta, 

 Nautilus, Conus, Cj'praa, Bulla, Voluta, Buccinum, Strombus, 

 Murex, Trochus, Turbo, Helix, Nerita, Haliotis, Patella, Den- 

 talium, Serpula, Teredo, and Sabella. 



It will now be proper, before proceeding to a description of 

 the generic characters of the Linnean system, to make the student 

 acquainted with the terms used in Testaceology, as far as regifds 

 the different parts of shells. 



EXPLANATION OF THE PARTS OF SHELLS. 



MULTIVALVE. 



Valves of Chitons. — Chitons in general have eight trans- 

 verse, broad, but very short valves, placed on the back of tha 



b2 



