REPOET ON THE ECHINOIDEA. 301 



Fig. 5. Somewhat older thau figs. 1-4, measuring 22 mm., seen from the ahactiual side. 

 ,, 6. Same, seen from the actiual side. 

 ,, 7. Same, seen in profile. 

 ,, 8. Same, seen facing the anal extremity. 



,, 9. Still older specimen, measuring 39 mm., seen from the abactinal side. 



„ 10. Same, seen from the actinal side. 



,, 11. Same, seen facing the anal extremity. 



,, 12. Same, seen in profile. 



„ 11'. Abactinal system and surrounding plates of specimen, measuring 16 mm. 



,, 12'. Abactinal system and surrounding plates of specimen, measuring 39 mm. 



,, 13. Interior view of apical system and genital organs of imperfect specimen, 



measuring about 50 mm. 



,, 14. Exterior view of apical system and surrounding plates (same as fig. 13). 



„ 15. Interior view of actinal system of imperfect specimen, measuring about 35 mm. 



„ 16. Exterior of same as fig. 16. 



,, 17. Interior view of actinal system of specimen, measuring about 25 mm. 



,, 18. Exterior view of same as fig. 17. 



,, 19. Interior view of anal system and termination of intestine of specimen measur- 



ino- about 35 mm. 



„ 20. Exterior view of anal system of same as fig. 19. 



PLATE XXIX^ 



Cystechinus ivyvillii, A. Ag. (figs. 1-9), p. 152. 



Fig. 1. Abactinal view of test, denuded ; natural size. 

 ,, 2. Same, seen from the actinal side. 

 ,, 3. Same, seen in profile. 

 ,, 4. Same, seen facing the anal extremity. 

 „ 5. Magnified view of plates surrounding the actinostome. 

 ,, 6. Interior view of same as fig. 5. 

 ,, 7. Interior view of the apical part of one of the lateral anterior ambulacra and 



adjoining interambulaeral plates. 

 ,, 8. Interior view from the actinal side, to show the course of the alimentary canal. 

 „ 9. Magnified view of one of the interambulaeral plates, to show the ridges and 



tuberculation. 



