WAX SIMULACRA OF SHELLS. 



Text-figure 3. 



233 



Comparison of form, markings, and structure in a mollusoan shell, and artificial 

 mitatiou of the same in paraffin-wax. 



A. Diagram of section of a Lamellibranch shell. The outer line represents the 



periostracum which is uucalcilied, and usually worn away except near 

 the growing edge, which is on the right of the diagram. The layer 

 indicated b3 r vertical strokes is the prismatic layer, the curved continuous 

 lines represent successive layers of the nacreous substance which lines the 

 inner surface of the shell. 



B. Section of a shell-like plate of paraffin-wax. The convex surface marked with 



depressions at regular intervals, is the lower surface in contact with the 

 water; the horizontal surface is the upper surface, exposed to the air. J 



Text-figure 4. 



Photograph of a ' shell ' in paraffin-wax resembling a Lamellibranch shell, 

 such as a cockle. 



