200 BRITISH ENTOMOSTRACA. 



The thorax and abdomen are very distinct from each 

 other ; the former being twice the size of the latter. The 

 thorax is composed of four segments, the abdomen of six ; 

 but, in the female, the second and third are so united as 

 to appear only one. The last segment terminates in two 

 lobes. The first segment of the thorax, to which the 

 head is immoveably fixed, and with which it is perfectly 

 consolidated, is much larger than any of the others, 

 being equal in size to all the other three; the second 

 and third are nearly equal in size, and the fourth is the 

 smallest. 



The antennae consist of numerous articulations, amount- 

 ing to twenty-six ; each articulation throws forward a seta, 

 sometimes two. In the male (t. XXIV, f. 1) they are shorter 

 than in the female, and they each possess a peculiar swelling 

 about the middle of their length, followed by a sudden 

 contraction, the first articulation of which forms a hinge- 

 joint. If we throw the animal into a state of semi- 

 asphyxia by placing it in a mixture of spuits of wine and 

 water, we perceive these antennee turn round in a con- 

 trary direction to what they ordinarily do when in their 

 native element, and curving their extremities at this 

 hinge-joint, they bend back the part beyond it upon the 

 swollen portion. The antennules are divided into four 

 . articulations (t. XXIV, f. a), each furnished with several 

 'setae ; the terminating one having six of unequal length. 



The mandibles (t. XXIV, f. h) are composed of three 

 parts, body, neck, and palpiform branch. 



The body is of an ovoid shape, convex on the upper, 

 and concave on the under surface, in which concavity is 

 lodged its motor muscle. The neck is a sort of petiole, 

 tm-ned upon itself, and dilated at its extremity, in which 

 are implanted six tolerably strong teeth. The palpiform 

 branch consists of one ring, and two long filaments. 



A little behind the mandibles we see the anterior, or 

 first pair of foot-jaws (t. XXIV, f. c), which are strong organs, 

 each composed of a pretty large body, convex externally, 

 and concave internally, giving origin to two processes, the 



