ON CRUSTACEA. 
233 
solid, lateral pieces, compressed, and trenchant internally, 
carrying on their back, and near their point of articulation, an 
appendage or palpus formed of three articulations ; these man- 
dibles being placed anteriorly, and underneath all the other 
even pieces : 3rd. with a thin, lamellate, and bifid tongue, 
placed against the posterior basis of the mandibles : 4th. with 
a first pair of jaws, membranaceous, deeply lobate, and ciliated 
on their edges, without palpi, and applied on the lower face of 
the mandibles : 5th. with a second pair of jaws, without palpi, 
applied on the first, equally membranaceous, lobate, and cili- 
ated : 6th, with a third pair of membranaceous jaws, provided 
externally with a palpus, formed of a long peduncle, which 
carries at its extremity a small arched stalk, setaceous and 
multi-articulate: 7th, with a fourth pair of jaws, formed by a 
stem rather narrow, compressed, not membranaceous, divided, 
like the feet, into six articulations, and by an external flagelli- 
form palpus, analogous to that of the preceding jaws, but more 
distinct : 8th. with a last pair of pieces, composed like the 
preceding, of two parts or stems ; the interior, crustaceous and 
compressed, is divided into six articulations, of which the second 
and third are much larger than the others, and the last small ; 
the exterior is in the form of a palpus similar to those of the 
two pair of jaws which are situated before these last. 
M. Savigny considers these three pair of external jaws as 
nothing but feet, so modified as to serve for manducation, and 
his opinion is founded upon this, that the palpus with which 
they are provided is analogous to the threads remarked in the 
anterior feet of many entomostraca, that the two external ones 
are articulated like feet, properly so called, and generally com- 
posed of the same nymber of pieces, and that at the base they 
serve as a point of attachment for the gills like ordinary feet. 
According to this naturalist, all the true Crustacea should have 
sixteen feet, and not differ among themselves, but in the 
number of those feet which are thus converted into auxiliary 
