42 MALACOZOA. GASTEROPODA. PULMOBRANCHIATA. 



in the upper part of the spire or cone ; but the head and 

 foot are protruded when the animal is in motion, and 

 retracted when at rest. In many species, a solid horny 

 or calcareous lid or operculum, which closes the aper- 

 ture of the shell, when the animal has retired into it. 

 Some species are terrestrial, but more are aquatic. Of 

 the latter most live in the sea, the rest in fresh water. 



Slugs, snails, welks, buccines, and other common 

 mollusca afford familiar examples of this order, any 

 species of which may be at once known by its fleshy disk 

 or foot. 



The Gasteropodous Malacozoa, being very numerous, 

 are divided into several orders : 1 . Pulmonata, or 

 Pulmobranchiata ; 2. Pectinibranchiata ; 3. Tubuli- 

 branchiata; 4. Scutibranchiata ; 5. Cyclobranchiata ; 6. 

 Inferobranchiata ; 7. Tectibranchiata ; 8. Nudibranchi- 

 ata; 9. Cirrobranchiata. 



SYNOPSIS OF THE ABERDEENSHIRE SPECIES. 

 ORDER I. GASTEROPODA PULMOBRANCHIATA. 



Respiratory apparatus a pulmonary cavity on the back, 

 opening by an aperture on the margin of the mantle 

 over the neck, on the right side. Individuals bisexual. 



Pulmobranchiata, Blainville. Pulmdnes, Lungs. 

 TEREESTRIA. Residing on land. 

 FAMILY I. LIMACINA. 



Body elongated, contractile, with a shield-like mantle 

 above, and united in its whole length with the foot be- 

 neath ; four retractile tentacula ; eyes on the summits of 

 the upper; generally no external shell, but an internal 

 thin scale in the mantle. 



