EXPLANATION OF THE PARTS OF SHELLS. 27 



Teeth of univalves, according to Colonel Montagu, are not 

 properly denticles, or tooth-shaped protuberances, but are 

 fine white laminae, or ridges, running spirally backwards, in a 

 pajallel direction to each other ; those on the exterior lip 

 may, in most instances, be traced through the outside of the 

 shell, and are nearly alike in length. Plate III. fig. 13, a. 



Epidermis is a skin, or cuticle, covering the exterior surface 

 of many shells of aU the orders, destined by nature to protect their 

 surface from being injured. It is membranaceous, somewhat 

 similar to the periosteum, which covers the bones of animals. 

 This substance is the production of the animal inhabiting the 

 shell ; it is uniformly observed in some species, and not at all 

 in others. Shells with a rugged or uneven surface have almost 

 always this epidermis. In some it is strong, laminated, velvety, 

 fibrous or rough, often beset with long hairs, and in others very 

 thin, smooth and pellucid, and admits the colours of the shell to 

 shine through it. In some species it is so dusky, that it entirely 

 obscures the beautiful colouring of the shell beneath. Although 

 many shells are very beautiful, even with this cuticle on them, 

 tbey are much more so when it is removed ; but I would by no 

 means advise the collector of shells to remove it, unless he may 

 have several duplicates of the same species ; and then he may 

 do it by way of variety. It is always preferable, however, to 

 keep tliem iti a state of natiu:e. 



A shell with epidermis is represented in Plate III. X;and 

 the effect of the epidermis removed at /. 



All other protuberances, furrows, &c. will be described at the 

 end of the work, in the Glossary of Terms used in the Science. 



The next thing to be taken into consideration, is the Linneaa 

 genera composing the three orders of shells. 



