72 
BRITISH ENTOMOSTRACA. 
rather of a complicated structure, is situate near the junc- 
tion of the head and body, near the base of the beak, and 
consists, according to Straus, who has given the most 
correct account of this organ, of a labrum or lip, two man- 
dibles, and one pair of jaws. The labrum or lip (f. b, 
g , and f. c) consists of a flattish body, compressed at the 
sides, and has at its extremity a large lobule, furnished 
with several setse. It is fixed to the posterior part of the 
base of the beak, is very moveable upon its antero-superior 
angle, and by means of powerful muscles (f. <j, a , b , c) admits 
of a considerable separation. 
The mandibles (f. d) are very strong, and consist each 
of a stout fleshy-looking body, which, at its superior extre- 
mity, is in form of a narrow point, and articulates there 
by means of several muscles with the body (f. a,/). It 
descends from thence vertically to the mouth, its inferior 
extremity being curved sharply inwards, so as to penetrate 
into the mouth between the lip and corresponding jaw, 
and terminates in a free unattached edge, which has appa- 
rently neither teeth nor triturating surface, but which 
when pressed closely between two pieces of glass, may be 
observed to be provided with a series of about eight small 
teeth, slightly curved. These mandibles are not provided 
with either palpi or branchiae, but are quite naked, and 
are moved by two muscles ; an abductor, which moves 
them upon themselves from within outwards, and an 
adductor, which brings them back to their first position, 
at the same time bringing them nearer, each to the other. 
The motion of these organs, when the animal is feeding, 
is semi-rotatory. 
The jaws (f. a, b, p, and f. p) consist each of a strong 
body, somewhat rounded on the anterior surface, and 
terminated by four strong horny spines, three of which 
are prolonged into hooks, strongly curved forwards and 
inwards. The fourth being small and straight. These 
parts seem to be constantly in motion, as if the animal 
were perpetually employed in eating. The mouth, as I 
have already stated, was placed by Swammerdam at the 
