MOLLUSCA OR UNIVALVES. 133 



PART IV. 



MOLLUSCA OK UNIVALVES.* 



The molluscs of univalve shells are all fur- 

 nished with a head, and a foot or fins, and are 

 divided into five orders, which are distinguished 

 from each other by the construction of the foot : 

 they are, — 1. Pteropoda], having fin-like feet 

 used for swimming. 2. Gasteropoda %, having the 

 foot proceeding from or covering the stomach. 

 3. Trachelipoda §, having it attached to that 

 part which lies between the head and body, or 

 neck. 4. Cephalopoda ||, having them (for there 

 are more than one) fixed to the head. And 5. 

 Heteropoda%, with feet or fins varying in dif- 

 ferent genera. 



In the annexed plan are shown, at one view, 

 the divisions and subdivisions of the order Mol- 

 lusca or Univalves ; but before entering upon 



* Les Mollusques, Lamarck. 



-j~ From pteron, Gr., a wing, and poda,feet. 



J From gaster, the stomach, and poda. 



§ From trachelo, the neck, and poda. 



|| From cephale, the head, and poda. 



1T From heteros, various, and poda. 



K 3 



