131 



simple and entire, whilst that of the other is characterized by a strongly 

 recurved canal.* 



The Turritella are apparently a strong muscular group of moUusks, the 

 disk being surmounted by a stout pedicle, by the strength of which the 

 shell is borne up at an angle, and not allowed to trail upon the ground, 

 as in the Cerithia and other elongated forms. MM. Quoy and Gainiard 

 also notice a peculiarity in the mantle, which is prolonged into a fringed 

 ring or collar, tlu'ough wliich the head passes in and out of the shell. 



The genus is somewhat limited in species compared with Cerithium or 

 Terehra, and the shells exhibit little variation of colour. They are all of a 

 more or less sombre hue, though none are very dark, but may be admired 

 on account of the beautiful symmetry of their graduated screw-like pro- 

 portions. 



The T^irritella. inhabit both the East and West Indies, and one or two 

 species occur on the coast of Senegal and New Holland. 



1 . acutangula, BesJuiyes. 



2. alternata. Say. 



3. australis, Lamarck. 



4. biciiigiilata, i«raarc/4'. 



5. bisuturalis, Say. 



6. brevialis, Lamarck. 



7. Broderipiana, D'Orb. 



8. cariiiifera, Lamarck. 



9. cingiilata, Boicerhy. 

 10. cornea, Lamarck. 



Species. 



11. duplicata, Lamarck. 



12. erosa, Courthouy. 



13. exoleta, Ijumarck. 



14. fuscata, Lamarck. 



15. granosa, Qnoy. 



16. iinbricata, Lamarck. 



17. impressa. Say. 



18. ligar, BesJmyes. 



19. mesal, BesJiayes. 



20. nodulosa, Kiny. 



21. replicata, Lamarck. 



22. rosea, Quoy. 



23. spii'ata, Sfmerby. 



24. terebra, Lamarck. 



25. tricar iuata, Kluy. 



26. trisulcata, Lamarck. 



27. ungulina, Beshayes. 



28. virginiaaa, Lamarck. 



Figure. 



TuKRiTELLA piCTA. Plate 11. Fig. 51. Shell, showing the symmetrical 

 screw-like convolution of the whorls and rounded aperture, with its 

 margin entire. — From Mr. Cimdng's collection. 



* If we make an actual comparison of the animal of Turritella with that of Turbo and 

 Trockns, we find the differences between them to be too ^cvA, to allow of their being any longer 

 maintained in the same family. By extending the comparison to the Cerithia, we immediately 

 recognise a much closer analogy between Turritella and that genus, than could be at first 

 imagined. The Cerithia are not zoophagous, as Lamarck believed ; their mode of living and 

 organization prove it. The comparison may be further extended to the MelanicB and Melanop- 

 sides which inhabit fresh water. I have already indicated (Encyclopedic Methodique) the 

 relation which may be traced between the Melaiiue and the Turritellce and Cerithia, and the 

 observations of MM. Quoy and Gaimard are confirmative of this opinion. To explain in a word 

 what 1 mean by a comparison, which is not, however, altogether exact, I may say that the 

 Melaiiiie are to the Turritelhe what the Neritince arc to the Neritce, and the Melano^mdes to 

 the Cerithia. — Deshayes, Anim. sans vert, vol ix. p. 250. 



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