ON THE MICROSCOPIC STRUCTURE OF SHELLS. 23 



calcareous prisms of outer layer of Pinna. Magnified 185 diameters 



(§7). 



Plate V. — Fig. 10. Section of Pinna nigrina, perpen dicular to the sur- 

 face, cutting the prismatic cells longitudinally. Magnified 185 dia- 

 meters (§11) Fig. 11. The same decalcified by immersion in acid; 



showing the residual membrane (§ 11). 



Plate VI. — Fig. 12. Various stages of cell-formation in Perna epliippiwmi 

 showing at a small cells (?) in incipient stage of development, imbedded 

 in intercellular substance ; at b, their development more advanced ; at 

 c, their polygonal form beginning to show itself; and at d, their com- 

 pletion, their walls coming into contact with each other, and the inter- 

 cellular substance disappearing. — Fig. 13. Various stages of cell-trans- 

 formation in the same shell ; showing at a the distinct cells ; at b, the 

 process oi fusion beginning to manifest itself; and at c, the fusion so far 

 advanced, that the partitions between the cells cease to be discernible, 

 except at the angles. Magnified 250 diameters. 



Plate VII. — Fig. 14-. Cells in external layer of 3Iya arenaria. Magnified 

 125 diameters (§ 3). — Fig. 15. Cells in external layer of Anatina olen. 

 Magnified 250 diameters (§ 17). — Fig. 16. Crystals in imperfectly-cal- 

 cified layer of Ostrea edulis. Magnified 350 diameters (§ 3). 



Plate VIII. — Fig. 17. Polished surface of Nacre, showing the lines by which 

 it is marked. Magnified 85 diameters (§ 22). — Fig. 18. Decalcified 

 membrane of the same, from Haliotis splendens, with the plaits undis- 

 turbed. Magnified 75 diameters (§ 25) Fig. 19. Basement- membrane 



of Nacre irregularly extended. 



Plate IX. — Fig. 20. Tubular structure oi Lima scabra. Magnified 200 dia- 

 meters (§ 30). — Fig. 21. Portion of the same, magnified 412 diameters. 

 — Fig. 22. Tubular structure of Lingula. Magnified 400 diameters 

 (§47). 



Plate X Fig. 23. Section of Hippurite — horizontal. Magnified 10 dia- 

 meters (§ 32). — Fig. 24. Section of Hippurite — vertical. Magnified 10 

 diameters (§ 32). 



Plate XI. — Fig. 25. Section of Pleurorhynchus Hibernicus, parallel to the 

 surface. Magnified 10 diameters (§ 34). — Fig. 26. Vertical and oblique 

 sections of ditto. Magnified 10 diameters (§ 34). 



Plate XII. — Fig. 27. Fractured surface of Terebratula (Atrypa) psittacea. 

 Magnified 125 diameters (§ 37).— Fig. 28. Thin shred of ditto. Mag- 

 nified 250 diameters (§ 38). 



Plate XIII. — Fig. 29. Internal surface of Terebratula (Atrypa) psittaeea. 

 Magnified 75 diameters (§ 39). — Fig. 30. Section of ditto, parallel to 

 the surface. Magnified 185 diameters (§ 39). 



Plate XIV. — Fig. 31. Section of Terebratula octoplicata, parallel to the 

 surface. Magnified 250 diameters (§ 42). — Fig. 32. Fractured surface 

 of ditto. Magnified 250 diameters (§ 42). '% 



Plate XV Fig. 33. Internal surface of Terebratula truncata. Magnified ~^ 



75 diameters (§ 40).— Fig. 34. Internal surface of Terebratula. Mag- ^ 

 nified 125 diameters (§40). . f~ 



Plate XVI Fig. 35. Horizontal section of Terebratula truncata. Magni- ^r 



fied 125 diameters (§ 41). — Fig. 36. Horizontal section of Terebratula -^ 

 bullata. Magnified 125 diameters (§ 41). ^ 



Plate XVII. — Fig. 37- Vertical section of Terebratula truncata. Magni- *i 

 fied 55 diameters (§ 41). — Fig. 38. Vertical section of Terebratula am- ^] 

 pulla. Magnified 125 diameters (§ 41). — Fig. 39. Vertical section of 

 Terebratula variabilis. Magnified 125 diameters (§41). 



