72 , BRITISH ENTOMOSTRACA. 



rather of a complicated structure, is situate near the junc- 

 tion of tlie head and body, near the base of the beak, and 

 consists, according to Straus, who has given the most 

 correct accoimt of this organ, of a hibrum or hp, two man- 

 dibles, and one pair of jaws. The labruni or lip (f. b, 

 (7, and f. c) consists of a flattish body, compressed at the 

 sides, and has at its extremity a lai'ge lobule, furnished 

 with several setae. 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 ]jowerful muscles (f.c, r/, h, c) admits 

 of a considerable separation . 



The mandibles (f. d) are very strong, and consist each 

 of a stout fleshy-looking body, Avliich, 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 the] ice 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, Avhich has appa- 

 rently neither teeth nor triturating surface, but wdiich 

 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, Avhen 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, Avas placed by Swammerdam at the 



