25 



larged, the shell, imbedded in the thickened mantle, has quite a rudimen- 

 tary appearance. The orifice of the shell is in such instances enlarged 

 according to the proportions of the animal. In another form of Fissurella, 

 allied to this, genus MacrocJdsma of Swainson, the fecal orifice is stretched, 

 so to speak, nearly to the anterior basal margin. Some of the Fissurella, 

 more especially those of conical form, have the vertex subspiral and a little 

 inflected, and in all there is an indication of this structure in an early 

 stage of growth. With the advance of growth the orifice becomes enlarged, 

 and the subspiral vertex disappears. 



The geographical range of the Fissurella is considerable, but the genus, 

 commencing with a single species on our own shores, F. reticulata, is but 

 poorly represented in the eastern hemisphere. The large gaily-painted 

 species inhabit the western coast of South America, and are found in com- 

 parative abundance from California down to Patagonia and the Falkland 

 Isles. 



Species. 



1. aculeata, Reeve. 



2. iEgis, id. 



3. sequalis, Sow. 



4. alabastrites, Reeve. 



5. alternata, Soy. 



6. aperta, Soio. 



7. aspera, id. 



8. asperella, id. 



9. atrata, Reeve. 



10. australis, Krauss. 



11. Balanoides, Reeve. 



12. Barbadensis, Sol. 



13. Candida, Sow. 



14. catillus, Reeve. 



15. Cayennensis, Lam. 



16. Ckemnitzii, Sow. 



17. clathrata. Reeve. 



18. ciypeus, Sow. 



19. coarctata, King. 



20. corapressa, Reeve. 



21. concinna, Phil. 



22. Conoides, Reeve. 



23. costata, Less. 



24. crassa, Lam. 



25. crenigera, Sow. 



26. crenulata, id. 

 VOL. II. 



