20 INTRODUCTORY EXPLANATION, ETC, 
A shell with epidermis is represented in Plate III. fig. XY; 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 BIVALVE SHELIS. 
Fig. 1. Hinge of the Unio pictorum, a Primary tooth, ¢ c¢ 
double teeth. 
Fig. 2. Hinge of the Solen. 6 Lateral teeth. 
Fig. 3. Hinge of the Lucina radula, a a Primary teeth, 2 car- 
tilage. 
Fig. 4. Hinge of the Cardium. 6 Lateral tooth, d d middle 
teeth, / Z spines. 
Fig. 5. Hinge of the Lutraria. 
Fig. 6. Inside of both valves of the Donax trunculus. A is 
the left valve, and B is the right valve, } lateral teeth, e primary 
complicated tooth, or cleft in the middle, m m crenulated margin. 
Fig. 7. Hinge of the Venus, a a Primary teeth. 
Fig. 8. Hinge of Spondyius gzederopus, f fincurved teeth. 
Fig. 9. Hinge of Isocardia Cor. 
Fig. 10. Hinge of the Pectunculus, k & numerous small teeth ; 
the distinguishing characteristic of the Family Arcacea. 
Fig. 11. Hinge of the Pecten, 2 cavity of the hinge, A superior 
ear, 7 inferior ear. 
Fig. 12. Hinge of Anomia Ephippium. 
