Nio'KERsoN. — Scales of Lepidosteus. 



PLATE IV. 



Fig. 23. Portion of section of scale and overlying tissue from a fish 460 mm. 



long. X 362. See description of Figure 22, Plate III. 

 " 24. Base of spine beginning to be imbedded in the outer layers of the scale. 



From fish 190 mm. long. X 370. 

 " 25. An oblique section through the base of a spine partly imbedded in the 



scale. From a fish 300 mm. long. X 387. 

 " 26. Section through a spine having an abnormally shaped tip. X 105. 

 " 27. Surface view of posterior e.xtremity of a scale freed from soft tissues by 



treatment with caustic potash, showing loosened cap on point of 



spine. X 75. 

 " 28. Longitudinal section through a scale of a fish 190 mm. long. X 44. 

 " 29. Longitudinal section through a scale of a fish 287 mm. long. X 25. 

 " 30. A representation of a portion of the surface of a scale of a fish 287 mm. 



long. The dotted lines show the positions of Haversian (or Volk- 



mann's) canals beneath the surface. X 31. 

 " 31. Outlines of several scales of a fish 300 mm. long. The dots indicate the 



positions of tl)e spines on four scales. X Gh 



