CLASSIFICATION OP GASTEROPODS. 



87 



O 



having lungs 



(ORDERS.) 

 { PULMONEA. 



... I 



in a dorsal 

 cavity, open 

 above the 

 head. 

 Shell 



Tubiform, J- TUBULIBRANCHIATA. 



Very open ; "j 

 ordinarily in [ 

 form of a 

 shield. 



8 



beneath a fold of the mantle, 1 

 which almost always con- I TKCTIBRANCHIATA 

 tains a shell, or beneath a f A 

 . straight edge of the foot, j 



{shell not turbi- f 

 nate; of one or > CYCLOBRANCHIATA. 

 more pieces, i 

 Without a shell } INFEROBRAJJCHIATA. 



{ upon the back. 



} NUDIBRANCHIATA. 



vertically compressed, and only fit for i HETEROPODA . 

 .swimming. ^ 



ORDER OF GASTEROPODA PUUKONEA. 



9. Gasteropods formed for aerial respiration have no branchiae, 

 but have a cavity on the back, upon the parietes of which the 

 pulmonary vessels form a complicated net-work (See fig. 21, 

 page 35), and the lung receives the external air through a hole 

 in the edge of the mantle above the right side of the nape, which 

 is susceptible of being opened or shut at the will of the animal. 

 All the pulmonic gasteropods are not however terrestrial mol- 

 lusks. Many of them live in the water; but then they are 

 obliged to come to the surface from time to time, to obtain air 

 necessary for their respiration. All these animals feed on vege- 

 table substances. 



10. The order of pulmonic gasteropods is divided into two 

 families ; the terrestrial pulmonea^ and the aquatic pulmonea. 



11. The FAMILY OF PULMONEA TERRESTRIA are general- 

 ly recognised with ease by their four tentacles. These append- 

 ages are retractile, and those forming the upper pair, which 



9. What are the general characters of the breathing apparatus of the 

 order of Ga'steropoda Pulmonea ? Upon what do they feed ? 



10. How is the order of pulmonic ga'steropods divided ? 



11. What are the characters of the family of terrestrial pulmonea? 



