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SUPPLEMENT 
jaws. These are what are designated in our text, by the ap- 
pellation, somewhat startling to the uninitiated, of jaw-feel. 
In the crabs, the external jaw-feet, or third auxiliary jaws 
of M. Savigny, are always very apparent. They close the 
mouth above, and cover all the space comprised by the buccal 
cavity. The second piece of their internal stem, the largest 
of all, is pretty generally applied by its interior edge, against 
the corresponding edge of the same piece, in the opposite 
jaw-feet, but sometimes these pieces are separated, and leave 
a triangular space between them. The third piece is smaller 
and of a form sometimes square, sometimes triangular, tra- 
pezoidal, or oblong, and its point, or internal edge, presents 
an emargination, for the juncture of the fourth articulation, 
which, itself, affords an attachment to the two last. 
The second, and especially the third, articulation of the 
external jaw-feet, present the most numerous modifications in 
their forms, and most usually serve to characterize the genera 
of the brachyurous decapods. In the long-tailed decapods, 
(astacini) the mandibles and the two genuine pair of mem- 
branaceous and lobate jaws, differ but little from the same 
parts in crabs. But the jaw-feet, and particularly those of 
the external pair, are elongated, prismatic, and strong. The 
final articulations are nearly as thick as the second and third, 
and these pieces have an incontestable analogy with the am- 
bulatory feet. In pasiphae and mysis they are visibly em- 
ployed in locomotion. 
The squillse of the order stomapods, Crustacea, very ano- 
malous in their organization, are provided with a large 
conical upper lip ; with two very strong mandibles, denticu- 
lated and palpigerous ; with a tongue formed of two com- 
pressed pieces, placed one on each side, and performing the 
office of jaws; with a first pair of membranaceous jaws com- 
posed of two pieces, and bearing, externally, a small palpi- 
form appendage ; with a second pair of foliaceous jaws, trian- 
