222 Lamarck's Genera of Shells. 



from the whorls being united in a discoidal form, makes it still 

 more like a planorbis. It differs from the Cleodora, merely by 

 being spiral. 



One Species. Limacina helicialis *. (Clio helicina. Gmel.) 

 Nortli Seas. Whales are said to prey on the Limacina. 



5. Cymbuliaf. 



Body oblong, gelatinous, transparent, enclosed in a shell. 

 Head sessile J ; two eyes ; two retractile tentacula ; mouth fur- 

 nished with a retractile trunk. Two opposite, rather large, 

 rounded oval, branchiferous alse, connected, at the posterior 

 base, by an intermediate, lobe-shaped appendix. 



Shell gelatino-cartilaginous, very transparent, crystalline, 

 oblong, in shape like a shoe, truncated at the summit; aperture 

 lateral, anterior. 



One Species. Cyrnbidia peronii\. 



Mediterranean, near Nice. Length about two inches. PL 

 VIL Fig. 109. 



6. Pneumodermon ||. 



This genus has no shell. 



Second Order. 

 Gasteropoda. (Contains 7 Families.) 



Body of the animal straight, never spiral, nor enveloped by 

 a shell, capable of containing it wholly ; a foot, or muscular 

 disk under the belly, united to the body nearly through its whole 

 length, and used in crawling. 



Some of the individuals of this order are naked, others have 

 a dorsal, but not enveloping shell, and others have an internal 

 shell, more or less hid under the mantle. 



The Gasteropoda are divided into seven families ; viz., Trlto- 

 iiiana, Phyllidiana, Semi-Phyllidiana, Calyptraciana, Bulls- 



* Resembling a helix. 



f From cijmhda, a Utile boat. 



X That is, without any distinct neck. 



§ Of M. Phon. 



II From vnivfAm, the lungs, and h^jta, the skin. 



