THE MOLLUSKS 273 



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

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



CLASSIFICATION OF MOLLUSKS 



CLASS I. Pelecypoda (Lamellibranchiata) . Soft-bodied unsegmented animals show- 

 ing bilateral symmetry. Bivalve shell, platelike gills. Examples : clam (Mya 

 arenaria), scallop (pecten), oyster (Ostrea), and fresh-water mussel (Unio). 



CLASS II. Gastropoda. Soft bodies asymmetrical ; 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. Bilaterally symmetrical mollusks with mouth sur- 

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

 altogether lacking (octopus). Examples : squid, octopus. 



REFERENCE BOOKS 

 ELEMENTARY 



Sharpe, A Laboratory Manual for the Solution 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 Mollusca," Cambridge Natural History. The Macmillan Company. 



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



Vol. XIX, page 193. 



Kellogg, The Shellfish Industries. Henry Holt and Company. 

 Parker, Elementary Biology. The Macmillan Company. 

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



HUNT. ES. BIO. 18 



