ANIMALIA MOLLUSCA. 105 



Romans bred them in parks, and fattened them for food; the 

 most esteemed came from Sicily and Africa. Snails breed 

 in all parts of the world ; moist localities are those in which 

 they assemble, through preference, during summer ; in winter 

 they bury themselves in the earth, or under walls, and the 

 bark of trees. 



ORDER II. NUDIBRANCHIATA. 



No shell nor pulmonary cavity ; branchiae exposed upon 

 some parts of the back. They are all marine animals, fre- 

 quently swimming in a reversed position, making the sur- 

 face of the feet concave like a boat, and aiding themselves 

 with the edges of their mantle and their tentacula as with 

 oars. Only one remarkable genus. 



GENUS DORIS, Cuv. 



Branchiae arranged in a circle on the posterior part of the 

 back, under the form of little arbusculse, composing altogether 

 the appearance of a flower. They are found in all seas. 

 Their ova resemble gelatinous bands spread upon rocks and 

 marine plants. 



ORDER III. PECTINIBRANCHIATA. 



Respiratory organs consisting almost always of branchiae, 

 composed of laminae, united in the form of combs, and con- 

 cealed in a dorsal cavity with a wide opening on the side of 

 the head. Almost all have turbinated shells, with the mouth 

 entire or provided with a syphon, and generally susceptible 

 of being more or less completely closed by an operculum at- 

 tached to the foot of the animal behind. Four remarkable 

 genera. 



GENUS I. CONUS, Lin. Cone. 



Shell conical, with the apex in front; the spire flat, or 

 slightly projecting; aperture rectilinear, very close, elongated, 



