THE MOLLUSKS 273 



summer months the oyster boats are to be found at work raking: the beds 

 for starfish, which aro collected and thrown ashore by the thousands. 



C'lassification of Mollusks 



Class I. Pclecypoda tLamellibranchiata) . yoft-bodied unsegmented aniraals show- 

 ing bilateral sjmmetr}-. Bivalve shell, platelike gills. Examples : clam (Mya 

 arenarid), scallop ^peclcii), oyster (Ostrea), and fresh-water mussel (Unio). 



Class II. Gastropoda. Soft bodies asj'mmetrical ; univalve shell or shell absent. 

 Some forms breathe by gills, others by lunglike sacs. Examples : pond snail, 

 land snail {Helix), and slug. 



Class III. Cephalopoda. Bilaterall>' s^-mmetrical mollusks with mouth sur- 

 rounded by tentacles. Shell may be external (nautilus), internal (squid), or 

 altogether lacking (octopus). E.xamples : squid, octopus. 



Reference Books 



ele.men'tary 



Sharpe, A Laboratory Manual for the Soltdion of Problems in Biology. American 



Book Company. 

 Davison, Practical Zoology, pages 142-150. American Book Company. 

 Heilprin, The Animal Life of our Seashore. J. B. Lippincott Company. 

 Jordan, Kellogg, and Heath, Animal Studies. D. Appleton and Company. 

 Morgan, Animal Sketches, Chap. XXI. Longmans, Green, and Company. 



ADVANCED 



Bulletin, U.S. Fish Commission, 1889. 



Brooks, The Oyster. Johns Hopkins Press. 



Cooke, "The MoUusca," Camliridge Natural History. The Macmillan Company. 



Kellogg, The Life History of the Common Clam. Bulletin, U.S. Fish Commission, 



Vol. XIX, page 19.3. 

 Kellogg, The Shellfish Industries. Henry Holt and Company. 

 Parker, Elementary Biology. The Macmillan Company. 

 Parker and Haswell, Textbook of Zoology. The Macmillan Company. 



HUNT. E8 BIO — 18 



