Lamarck's Genera of Shells. 219 



them inhabit the sea ; others live in fresh water ; and others, 

 again, in moist, shady places, on laud. Some of the latter, 

 however, are capable of supporting the heat of a brilliant 

 sunshine. 



This class is divided into the five following orders : 



First Order. 

 Pteropoda *. 

 No foot, or arm, for crawling or seizing its prey. Two oppo- 

 site and similar fins, (nageoires,) adapted for swimming. Body 

 free, floating. 



Second Order. 

 Gasteropoda f. 

 Body straight, never spiral, nor enveloped in a shell ca- 

 pable of containing the whole of it. Foot muscular, united 

 to the body nearly through its whole length, situated under the 

 belly, and formed for crawling. 



Third Order. 

 Trachelifoda J 

 Body in great measure spiral, separate from the foot, and 

 always covered by a spirivalve shell. Foot free, flat, attached 

 to the inferior base of the neck, and formed for crawling. 



Fourth Order. 



Cephalopoda §. 



Body, except the head, contained in a bag-shaped mantle. 



Head projecting beyond the bag, crowned with inarticulated 



arms, furnished with air-holes, and surrounding a mouth with 



two horny mandibles. 



Fifth Order. 

 HeteropodaIJ. 

 No coronet of arms on the head ; no foot, for crawling, under 



* From 'oli^tiv, a wing, and -sTtr;, a foot. 

 f From yajluf, tlie belly, and -nTtfc, a foot. 

 J From Tjaj^nXit, tlic neck, and -07^5, a loot. 

 $ From xE<))aAu, the head, and -aiag, a ioot. 

 g From ilsfoj, different, and wag, a foot. 



