PLATE VIII 

 VARIOUS DEVICES FOR EXCLUDING ENEMIES 



A. By closing the Aperture with a Separate Shelly or 

 Horny Operculum 



i. Pontatias elegans, Mull, (crawling), showing the position of the 

 operculum (shelly) on the upper side of the " tail." 



2. Vivipara contecta, Millet, showing the operculum (horny) com- 

 pletely closing the mouth of the shell. 



3. Strombus auris-Diancs , Linn., showing reduced operculum (horny) 

 forming a "claw" at the end of the foot for use in locomotion: 

 /., foot (folded) ; m., margin of mantle ; 0., operculum; p., proboscis 

 between the eye-stalks ; 5., siphon. 



4. Operculum of Struthiolaria. 

 5 to 10. Types of operculum : 



5. Claw-shaped, or unguiculate. nucleus apical, as in Turbin- 



ella, Fusus, etc. 



6. Turrited-spiral, as in Architectonica, etc. 



7. Imbricated, or lamellar, nucleus marginal, as in Purpura, 



Xenophora, Paludomus, etc. 



8. Multispiral, as in Trochus, et' . 



9. Paucispiral, as in Littorina, etc. Always sinistral in 



dextral shells. 

 10. Articulated, having a projection that fits round the colu- 

 mella, as in Nerita, etc. 



11. Operculum of Turbo fluctuatus, Reeve, outer surface. 



12. Operculum of Turbo sarmaticus, Linn. : a, inner surface; b, outer 

 surface. 



13. Operculum of Imperator olivaceus: a, inner surface; b, outer 

 surface. 



B. By Development of Teeth in the Aperture 



14. Polygyra hirsuta, Say. 



15. Anostoma globulostim, Lamk. 



16. Pythia plicata, Fer. 



C. By an Internal Spring Door 



17. Clausilia, sp., with portion of shell-wall removed to show the 

 clausium. 



D. By a Special Adaptation of the Shell Itself 



18. 19. Thyrophorella Thomensis, Greeff, in which the aperture of the 

 shell is closed by drawing down a hinged portion of the upper shell 

 wall (after Gerard). 



%* Figs. 17 to 19 drawn by Miss G. M. Woodward. All the rest by 

 S. P. Woodward. 



