TERRESTRIAL. 



THE Slugs and Land-Snails, which (as I before observed) 

 constitute about three-fourths of the British Pulmono- 

 branch Mollusca, may be conveniently divided into two 

 sections. The first section agrees in all essential particu- 

 lars, except that of having retractile (instead of contrac- 

 tile) tentacles, with the aquatic family of Z^mwcewZcB, which 

 have been above described. The second corresponds with 

 the Pectinibranch Mollusca in having separate sexes, 

 their eyes at the base of the tentacles, and univalve spiral 

 shells which are furnished with opercula ; and the main 

 point in which it differs from that great Order consists 

 in the organs of respiration, resulting from the nature 

 of their respective habitats. All the land Pulmono- 

 branchs are more slimy than their aquatic representa- 

 tives ; and they appear to be less inactive in their habits. 



The first section comprises four families, viz., 



* Tentacles, almost in every case, 4 : eyes placed on the tips 

 of the upper, or single, pair : shell rudimentary, shield- 

 like, or complete and spiral. 



I. LlMACID^E. 



II. TESTACELLIDJG. 

 III. 



** Tentacles 2, besides rudiments of a second or lower pair : 

 eyes placed at the internal base of the developed pair : 

 shell spiral, elongated. 



IV. CARYCHIID^E. 



