NiCKERSON, — Scales ol' Lepidosteus. 



PLATE III. 



Fig. 17. Section through axis of a spine showing the difference in appearance 

 between the superficial bony layers of the scale and those lying 

 deeper. From fish 190 mm. long. X 370. 



" 18. An abnormally shaped spine tip. X 370. 



" 19. Fibrillar appearance of the under surface of a scale from a fish 287 mm. 

 long, after treatment with caustic potash. X 275. 



" 20. Section through anterior edge of a scale from a fish 190 mm. long ; show- 

 ing fibres of connective tissue in the scale. X 275. 



" 21. Portion of ground section of scale of fish 300 mm. long. X 152. 



" 22. Portion of section of scale and overlying tissue from a fish 460 mm. long. 

 X 198. In a ground section of an immediately adjacent scale the 

 ganoin layer on the corresponding part was 12-15^ thick. Both in tiiis 

 and the succeeding figure (Plate IV. Fig. 23) an odontoblast is shown 

 lying upon the upper surface of the scale and sending its process down 

 through the ganoin layer m a dentinal tubule. 



