ORDER HETEROPODA. 51 
ATLANTA, Lesueur. 
These mollusca, according to the recent observations of M. 
Rang, should belong to this order. Their shell, instead of 
being widened like that of the carinariz, has a narrow cavity, 
spirally convoluted on one plane; its contour is raised by a 
thin crest. 
They are extremely small shells, from the Indian Ocean, in 
one of which Lamanon thought he had discovered the original 
Cornu ammonis. Atlanta Peroniti and Atlanta Keraudrenii, 
Lesueur, Journ. de Phys. Ixxxv. November, 1817, and Rang. 
de la Soc. d@’Hist. Nat. tome. III. p. 373, and pl. ix. 
N. B. We must not confound the Atlante of Lesueur with 
the Atlas described by him in the same place, and which, so 
confined is his description, I do not know where to class. 
Firona, Peron. 
The body, tail, foot, gills, and visceral mass, as in the cari- 
nariz, but no shell has ever been observed; the snout is 
elongated into a recurved proboscis, and the eyes are not pre- 
ceded by tentacula. From the end of the tail is frequently 
observed to proceed a long articulated filament, which Forskal 
took for a tenia, and the nature of which is not yet very clearly 
understood. 
One species, the Pterotrachea coronata, Forskal, Peron, 
Ann. du Mus. XV. ii. 8, is very common in the Mediter- 
ranean ; and M. Lesueur describes several from the same sea, 
which he considers as different, Journ. Acad. Nat. Soc. Philad. 
vol. i. p. 3, but which require further comparison. (Lrola 
mutica, F. gibbosa, &c.) 
M. Lesueur distinguishes the FIROLOIDE, where the body, 
instead of terminating in a compressed tail, is abruptly trun- 
cated behind the visceral bundle.—Jbid. p. 37. (Firoloida, 
Demaresiia, &c.) 
