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CLASS CRUSTACEA. 
The species whose testa is transverse, with the middle of 
the sides greatly prolonged, or dilated in the manner of a 
cylinder, or cone, form his genus Ixa> ( Leucosia cylindrus , 
Fab.) 
Those whose testa is rhomboidal, with seven conical 
points, in the form of spines, on each side, compose that of 
Iphis. 
If the testa, having always the same rhomboidal form, 
presents only angles or sinuses on the sides, we shall have his 
genus Nursia ; and that of Ebalia , if these lateral edges 
are smooth. 
The leucosiae, with ovoid, or almost globular testa, and dis- 
tinguished besides from many of the preceding, by having the 
claws always longer than the body, and thicker than the other 
feet, and the tarsi sensibly striated, may be thus divided. 
Some have the point advanced beyond, or at least not out- 
edged by the superior extremity of the buccal cavity. The 
external branch of the exterior jaw-feet is elongated, and 
almost linear. In these the claws are slender, with the hands 
cylindrical, and the fingers long. 
Sometimes the testa is almost globular, and either very 
spiny, as the genus arjcania , or even as in that of ilia . 
Sometimes the testa is suborbicular and depressed, as in 
the genus persephona ; or it is ovoid, as in that of myra . 
In some the claws are thick, with the hands ovoid, and short 
fingers. These are the true Leucosm of this naturalist. 
In the others, the superior extremity of the buccal cavity 
passes the front or forehead. The external branch of the ex- 
terior jaw-feet is short and arched; the testa is rounded and 
depressed. 
This last division comprehends his genus phylira. 
Other considerations, taken from the proportions of the feet, 
and the form of the external jaw-feet, support these characters. 
Ilia nucleus , Leach. 
