Dr. W. Baird on British Entomostraca. 85 



of a single joint at the base Mhich divides into two branches, 

 each having three joints. They are much shorter in all the 

 species than in the Daphnice. In the Jamellatus'^- the anterior 

 branch sends off from the last joint three long filaments or 

 bristles and a short one, and one from the extremity of the se- 

 cond and first joints, -while the posterior branch sends off only 

 three long ones and a short one from the last joint. The long 

 setae or filaments are each furnished "\vith a joint near the 

 centre as in Daphnia jmlex, and as in it also, are beautifully 

 plumose, Avhile the short ones are neither jointed nor plumose. 

 The use of these organs is the same as in the Daphnia, being 

 chiefly organs of locomotion. The brain apparently is the 

 same in situation and shape as in the Daphnics. The month 

 also is nearly of the same construction. The mandible (PI. II. 

 f. 5.) is a strong organ, articulating superiorly with the body 

 by a sharp and pointed extremity, whilst the inferior extremity 

 is free and unattached, curved a little inwards and rounded 

 somewhat at the tip, which is furnished with sevei'al strong 

 teeth. The jaws consist each of a strong large jjlate articu- 

 lating with the body by the narrow end, to which are attached 

 the muscles which move it. About the centre of its length 

 it takes a sudden curve and descends in the form of a broad 

 plate, which is slightly lunated at the extremity, the edges 

 terminating in sharp points. To the louer edge of its supe- 

 rior extremity is attached a flat squarish plate, which moves 

 simultaneously with the other part and to which it seems 

 firmly fixedf. These organs may be seen almost constantly 

 in motion when the animal is stationary, the motion of the 

 mandibles being pretty quick and oscillatory, wb.ilst that of 

 the jaws is slow, upwards and downwards. Part of the di- 

 gestive canal may be seen also in this upper part of the ani- 

 mal, commencing as in the DapJinioe immediately behind the 

 mouth in the form of an oesophagus and terminating in the 

 stomach, which is situate in the lower portion or body of the 

 shell. The stomach differs somewhat from that organ as seen 

 in the Daphnics, being curved or twisted into one or two com- 

 plete convolutions near the centre (PI. II. f. 6.). The body of 

 the animal is quite free and unattached within the valves of the 

 shell, except at the superior portion v/here we see it attached 

 to the posterior edge of the shell by about three broadish 

 muscles. It terminates superiorly in a point near the root of 

 the antennae, and almost upon the extremity of this point is 

 situate the black spot in front of the eye. A short distance 

 from this the body has an indentation, in which, or rather on 

 its edge, is situate the eye, already described. It then takes 

 a round turn, the edge of v.hich is more or less crenated, and 

 * Etirycercus lameUatiis, neb. Vide PI. II. fig. 4. f PI. II. fig. 12. 



