QUESTIONS ON UNIVALVES. 141 



in which the shell of the Cypraea is formed, and 

 increased in size ? 



18. What is the generic character of the 

 Bulla, and what its distinguishing mark ? 



19. What remarkable organ is possessed by 

 the animal of the Bulla? Describe the organ 

 and its use. 



20. Describe the peculiar habits of the animal 

 of Bulla Fontinalis. 



21. Give the generic character of the Voluta, 

 and its distinguishing mark. 



22. Into what different families is the Voluta 

 subdivided, and how are they distinguished ? 



23. W r hat is the generic character of the Buc- 

 cinum, and its distinguishing marks 1 



24. Describe the different groups into which 

 the genus Buccinum has been subdivided. 



25. What is the origin of the name Bucci- 

 num? 



26. What use has been made of the Bucci- 

 num? 



27. Describe the habits of the Hermit Crab. 



28. What is the generic character of Strom- 

 bus, and what its most characteristic mark ? 



29. Describe how the shells called Alatae, or 

 winged Strombi, are increased at the different 

 stages of the animal's growth. 



30. What is the generic character of the 

 Murex, and what is its distinguishing mark ? 



31. Describe the different families into which 

 the genus Murex is subdivided, and mention 

 how the forms of these shells are connected with 

 the peculiar habits of their animals. 



