234 SUPPLEMENT 



jaws. These are what are designated in our text, by the ap- 

 pellation, somewhat startling to the uninitiated, oi jaiv-feet. 



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, 

 iastacini) the mandibles and the two genuine pair of mem- 

 branaceous and lobate jaws, differ but little from the same 

 j)arts 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 squillae 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 

 ofBce 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- 



