PLATE CXXXIII. 
Fic, 
1. Rudimentary left operculum of Hydroiwes norvegica, Gunner. Enlarged. 
la. Tubes on a valve of Pecten. Somewhat enlarged. 
1. Trifid bristle (anterior). x oc. 4, obj. D. 
2. Tube of a variety of Placostegus tridentatus, Fabr., from the “ Porcupine” Expedition 
of 1870. 
3. Collar-bristle of Spirorbis medius, Pixell. x oc. 4, obj. F. 
3a. Winged bristle. x oc. 4, obj. D, with 2-in. draw-tube. 
3b. Geniculate bristle of the posterior region. X oc. 4, obj. F, with 2-in. draw-tube. 
3c. Hook. x oc. 4, obj. F. 
4. Operculum of variety of Placostequs tridentatus, J. C. Fabricius. Enlarged. 
5. Tube of Spirorbis heterostrophus, Montagu, from England. Enlarged. 
6. Tube of Spirorbis carinatus, Montagu. Hnlarged. 
7. Shorter posterior bristle of Spirographis Spallanzaii, Viviani. xX oe. 4, obj. D. 
7a. Longer bristle (anterior). x oc. 4, obj. D. 
7b. Anterior hook.  X oc. 4, obj. D. 
7c. Posterior hook.  X oc. 4, obj. D. 
8 and 8a. Collar-bristles of Spirorbis Pagenstechert, De Quatrefages, the latter seen 
antero-posteriorly so as to show the double web at the base. x oc. 4, obj. F. 
9. Long posterior bristle (winged) of Huchone rubrocincta, Sars. x oc. 4, obj. D. 
9a. Posterior hook. x oc. 4, obj. F. 
10. Long simple bristle of Apomatus ampulliferus, Philippi. & oc. 4, obj. D, with draw- 
tube. 
11. Hook of Spirorbis borealis, Daudin. x oc. 4, obj. F. 
12. Operculum of Spirorbis granulatus, L., St. Andrews. Hnlarged. 
12a. Branchial filaments. Enlarged. 
13. Operculum of Spirorbis medius, Pixell, Blacksod Bay. Enlarged. 
13a. Tip of branchial filament. Enlarged. 
14. Operculum of Spirorbis violaceus, Levinsen, var. Caulleryi, Mcl. oc. 2, obj. A. 
15. Sand-tubes of Sabellaria alveolata, L., showing funnel-shaped apertures. Slghtly 
enlarged. 
16. Operculum of Lilograna implexa, Berkeley. Magnified. 
17. Anterior hook of Amphicora fabricia, O. F. Miller. x oc. 4, obj. D, with full draw- 
tube. . 
18 and 18a. Anterior bristles of Nerinides longirostris, De Quatrefages. x oc. 4, obj. D. 
18). Hook. X oc. 4, obj. D. 
19. Hook of Nerinides tridentata, Southern. x oc. 4, obj. D. 
