20 CLASS PTEROPODA. 
The known species (Clio helicina of Phips and Gm.) 
Argonauta arctica, Fab., Faun., Groen., 387, is but little less 
abundant than the Clio Borealis in the icy sea, and is also 
considered as one of the principal aliments of the whale. 
HYALEA, Lam. CAvouina, Abild., 
Have two very large wings, no tentacula, a mantle cleft at the 
sides, lodging the gills in the bottom of its fissures, and in- 
vested with a shell likewise cleft at the sides, whose central 
face is very gibbous, the dorsal plate larger than the other, and 
the transverse line which unites them behind provided with 
three short denticulations. In the living state the animal puts. 
out, through the lateral clefts of its shell, some stripes, more or 
less long, which are productions of the mantle. 
The most known species (Anomia tridentata, Forskahl ; 
Cavolina natans, Abildgard ; Hyalea cornea, Lam.), Cuv., 
Aun. du Mus. IV. pl. lix., et Péron, ib. XI. pl. iii., fig. 13, has 
a small yellowish shell, semi-transparent, and is found in the 
Mediterranean and the ocean. 
CLEODORA, Péron, 
For which Brown originally created the genus Clio, appear 
analogous to hyalea, in the simplicity of their wings and the 
absence of tentacula between them. It is probable that their 
gills are also concealed in their mantle. Nevertheless, their 
conical, or pyramidal shell, is not cleft upon the sides. 
M. Rang distinguishes the CLEODORA, proper, with pyra- 
midal shell. 
CRESEIS with conical elongated shell. 
CUVIERIES with cylindrical shell. 
PSYCHE with globular shell. 
EuRYBIA with hemispheric shell. 
It has been thought we may approximate to hyalea, 
