20 INTRODL'CTION. 



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, they 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 them in a state of nature. 



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

 effect of the epidermis removed at 7. 



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

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



DESCRIPTION OF PLATE IV. 



HINGES OF BIVALVE SHELLS. 



Fig. 1. Hinge of the Unio pictorum, a Primary tooth, c c 

 double teeth. 



Fig. 2. Hinge of the Solen. h Lateral teeth. 



Fig. 3. Hinge of the Lucina radula, a a Primary teeth, n 

 cartilage. 



Fig. 4. Hinge of the Cardium. b Lateral tooth, r/ J middle 

 teeth, 1 1 spines. 



Fig. 5. Hinge of the Lutraria. 



Fig. 6. Inside of both valves of the Dcnax trnncnlus. A is 

 the left valve, and B is the right valve, b lateral teeth, b primary 

 complicated tooth, or cleft in the middle, m m crenulated margin. 



Fig. 7. Hinge of the Venus, a a Primary teeth, b lateral 

 tooth. 



Fig. 8. Hinge of Spo7iJijhis gsedcropus,ff'mcuT\edi teeth. 



Fig. 9. Hinge of Isocardia Cor. 



Fig. 10. Hinge of the Pectunculus, k k numerous small teeth ; 

 the distinguishing characteristic of the genus Area. 



Fig. 1 1. Hinge of the Pecten, g cavity of the hinge, h supe- 

 rior ear, i inferior ear. 



Fig. 12. Hinge of Anomia Ephippiiim. 



