144 . UNIVALVES. 



32. Which are the shells anciently called 

 Purpurae ? 



33. Describe tfie manner in which the purple 

 dye was obtained and prepared, the different 

 uses to which it was applied, and the circum- 

 stance supposed to have led to its discovery. 



34. What is the generic character of the 

 Trochus, and what its most distinguishing mark ? 



35. Describe a remarkable peculiarity in one 

 species of Trochus 



36. What is the generic character of Turbo, 

 and its distinguishing mark ? 



37. Which species of Turbo is remarkable, 

 and on what account ? 



38. What is the generic character of Helix, 

 and by what mark is it particularly distin- 

 guished ? 



39. What variety of form is displayed in the 

 Helices ? 



40. Detail the interesting facts connected 

 with the natural history of the Helix. 



41. How does the Helix lanthina display the 

 compensatory providence of God ? 



42. What is the generic character of the 

 Nerita, and by what mark is it readily known ? 



43. What is the generic character of the 

 animal inhabiting the Haliotis ? 



44. What is known of the habits of the 

 Haliotis, and what is its distinguishing mark ? 



45. What is the generic character of the 

 Patella, and what its most distinguishing 

 mark ? 



