Plate 47. 



1-11. Arbacia Dufresnii Gray. 



1. Tridentate pedicellaria. x 30. 



2. Ophicephalous pedicellaria. x 30. 



3. Triphyllous pedicellaria. X 30. 



4. Upper end of stalk of ophicephalous pedicellaria. x 70. 



5. Valve of tridentate pedicellaria. X 70. 



6. Valve of triphyllous pedicellaria. X 70. 



7. Valve (b) of ophicephalous pedicellaria. X 70. 



8. Basal part of second valve (a) of same ophicephalous pedicellaria. x 70. 



9. Basal part of third valve (c) of same ophicephalous pedicellaria. x 70. 



10. Sphaeridium. X 70. 



11. Calcareous plates from gills. X 70. 



12-16. Tetrapygus niger Agass. 



12. Valve of tridentate pedicellaria. x 70. 



13. Upper end of stalk of ophicephalous pedicellaria. X 70. 



14. Valve of ophicephalous pedicellaria. x 70. 



15. Sphaeridium from a small individual. X 70. 



16. Sphaeridium from a large individual. X 70. 



17-19. Arbacia punctulata Gray. 



17. Spha3ridium. x 70. 



18 Upper ends of stalks of ophicephalous pedicellariae. X 70. 

 19. Calcareous plates from gills. X 70. 



