PLATE XXVI. 



1. Exterior portion of a joint near the middle of Fig. 5. Plate XVIII. 



2 Distal face of the joint of Fig. 1, showing the formation of circular rings in the central part of 



the face of the joint. 



:i. Magnified segment of part of same face as Fig. 2. 



■1. Oblique view of radiating lamella; near outer edge of Fig. 3. 



•"). Distal face of the fourth joint from upper end of Fig. 9, Plate XVIII. 



6. Magnified segment of same face as Fig. 5. 



7. Transverse optical section of joint (Fig. 1), showing arrangement of the reticulation in irregular 



curved lines, extending from one face to the other. 

 B M ignified view of the calcareous reticulation of the inner part of the joint. 



noent of face of ring, three joints from the lower end of Fig. 9, Plate XVIII The radiating 

 ridges have become irregularly radiating lamellae, which are not continuous from the periphery 

 to the central axial canal. 



10. ' tblique view of a part of the outer edge of the face of the same ring. 



11. Part of suture of upper joints of Fig. 11, Plate XVII., greatly magnified. 



