520 HABITS OF ATLANTA. 



which were of singular forms, and, in general, of a steel 

 colour. Among the pelagic heteropodous Mollusks, which 

 we found, in crossing the South Atlantic ocean, were vast 

 numbers of Atlanta, and numerous Carinariae. They are 

 crepuscular animals, like the Pteropods, and are furnished 

 with hyaline shells, of the greatest delicacy and beauty. 

 The Atlanta, with an elegant, glassy, spiral, carinated 

 shell, globose in one species, and flattened in the other, 

 is quite a sprightly little Mollusk, probing every object 

 within its reach by means of its elongated trunk, twisting 

 its body about, and swimming in every direction, by the 

 lateral movements of its vertical, dilated foot. I have 

 frequently seen them descend to the bottom of the glass 

 vessel in which they were kept, fix themselves there in 

 the manner of a leech, by their sucking disc, and carefully 

 examine the nature of their prison-house, by protruding 

 the front portion of the foot in every direction. The 

 shell of the globose species (Helicophlegma Keraudrenii of 

 D'Orbigny,) is nearly membranous, and becomes opaque 

 and shrivelled on exposure to the air; the compressed 

 species (Atlanta Peronii of Lesueur,) has a firmer and 

 more vitreous shell. Lamanon, one of the Naturalists who 

 accompanied La Perouse, considered the Atlanta to repre- 

 sent the shells of those extinct fossil shells the Ammonites, 

 to which, however, it has but a faint resemblance. Al- 

 though it is perfectly true that pelagic Mollusks generally 

 swim on their backs, in a reversed position, as lanthina, 

 Firola, Carinaria, and Atlanta, yet, in figuring them, the 

 analogy of the parts is better represented by placing them 

 in the position most common to animals of this class. 

 Thus the species of Scyllaa, Doris, &c., are never repre- 



