Plate XVI. 



Fig. i. Interambulacral area of Stereocidaris ingolfiana. ~ ,. 

 2. — — - Echinus acutus, var. Flemingii. l j 1 . 



— 3. Apical area of Echinus elegans. 2 / r . 



a. — — - Strongylocentrotus drebachiensis. 2 / 1 . 



c — — - Echinus a cuius, var. norvegicns. 2 ,. 



_ 6. — - affinis. z /i- With two pores in one of the genital plates. 



7. — — - esculentus. 2 j 1 . 



8. — - Alexandri. 2 /i- With two pores in two of the genital plates. 



g. — — - Strongylocentrotus drebachiensis. 2 t . 



— 10. — — - Echinus acutus, var. Flemingii. 2 / 1 . 



— 11. Interambulacral area of Strongylocentrotus drebachiensis, £ granulans. 2 t . 



— 12. Plates from the buccal membrane and the gills of Echinus esculentus. a. b. from the buccal 



membrane outside the buccal plates, c. from inside the buccal plates, d. e. f. from the 

 gills. Obj. II. Oc. III. 



— 13. Plates from the buccal membrane of Strongylocentrotus drebachiensis. a. outside, b. inside the 



buccal plates. Obj. II. Oc. III. 



— 14. Plate from the buccal membrane of Parechinus microtuberculatus. Obj. II. Oc. III. 



— 15. - — — - — miliaris. Obj. II. Oc. III. 



— 16. Plates from the buccal membrane and the gills of Echinus acutus, var. Flemingii. a. b. from 



the buccal membrane outside the buccal plates, c. from inside the buccal plates, d. e. f. from 

 the gills, a. b. Obj. II. Oc. I., c.-f. Obj. II. Oc. III. 



— 17. Interambulacral area of Strongylocentrotus drebachiensis, i. pallidus. 2 / x . 



— 18. Ambulacral area of Echinus acutus, vox. -Flemingii. I / I . 



— 19. — - elegans. 2 / s . 



— 20. — — - affinis. 2 j t . 



— 21. — - Strongylocentrotus drebachiensis, f. granulans. 2 / s . 



— 22. — — - Echinus acutus, var. norvegictts. 2 / r . 



- 23. — - Strongylocentrotus drebachiensis, f. pallidus. - t . 



