PLATE XLIII. 



FIG. i. Spirorbis asperatus sp. nov., p. 245. Front view of operculum show- 

 ing calcareous plate. 



2. Front view of a calcareous plate from another operculum. 



3. Back view of same. 



4. Spirorbis semidentatus sp. nov., p. 237. Calcareous plate from oper- 



culum. 



5. Top view of same. 



6. Spirorbis eximius sp. nov., p. 239. Calcareous plate from operculum 



of type, from Pacific Grove, California, bottom view. 



7. Spirorbis asperatus sp. nov., p. 245. Back view of a calcareous plate 



from a smaller operculum. 



8. Spirorbis sulcatus (Adams), p. 249. Front view of calcareous plate 



from operculum of specimen on Haliotis from Guernsey, England. 



9. Spirorbis spirillum Linne", p. 243. Calcareous plate from operculum 



of specimen from Sitka, front view. 



10. Back view of same. 



11. Spirorbis eximius sp. nov., p. 239. Calcareous plate of operculum from 



type, nearly side view. 



12. Spirorbis semidentatus sp. nov., p. 237. Operculum showing calca- 



reous plate. 



13. Spirorbis asperatus sp. nov., p. 245. Side view of an operculum 



showing calcareous plate. 



14. Spirorbis quadrangularis Stimpson, p. 241. Operculum showing 



eggs and calcareous plate, from Greenland. 



15. Operculum, in profile, from specimen from Alaska. 



16. Spirorbis variabilis sp. nov., p. 238. Calcareous plate from operculum, 



to show the separation of two disks. 



17. Spirorbis eximius sp. nov., p. 239. Front view of operculum showing 



calcareous plate. 



18. Spirorbis formosus sp. nov., p. 251. Operculum of a medium sized 



animal, with empty calcareous cylinder. 



19. Spirorbis sulcatus (Adams), p. 249. Back view of fig. 8. 



20. Spirorbis stimpsoni Verrill, p. 250. Operculum showing primary 



calcareous plate. 



2 1 . Another operculum filled with embryos, with secondary calcareous plate. 



22. Back view of fig. 20. 



23. Spirorbis formosus sp. nov., p. 251. Posterior portion of operculum 



showing renewal of plate. 



24. Spirorbis abnormis sp. nov., p. 245. Back view of fig. 28. 



25. Spirorbis formosus sp. nov., p. 251. Operculum showing calcareous 



cylinder filled with embryos. 



26. Spirorbis asperatus sp. nov., p. 245. Front view of calcareous plate 



from a small operculum. 



(344) 



