20 INTRODUCTORY EXPLANATION, ETC, 



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

 the effect of the epidermis removed. 



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 BITALVE SHELLS. 



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

 double teeth. 



Fig. 2. Hinge of the Soleii. b Lateral teeth. 



Fig. 3. Hinge of the Lucina radula, a a Primary teeth, 7i car- 

 tilage. 



Fig. 4. Hinge of the Cardium. b Lateral tooth, d d middle 

 teeth, 1 1 spines. 



Fig. 5. Hinge of the Lutraria. 



Fig. 6. Inside of both valves of the Donax trvnculvs. A is 

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

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



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



Fig. 8. Hinge of Spoiidyliis gxderopjis, ffincnrved teeth. 



Fig. 9. Hinge of Isocardia Cor. 



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

 the distinguishing characteristic of the Family Arcacea. 



Fig. 11. Hinge of the Pecten, 5- cavity of the hinge, h superior 

 ear, i inferior ear. 



Fig. 12. l^mge oi Anoinia Ephippium. 



