46 BRITISH ENTOMOSTRACA. 



The jaws (t. V, f. a) consist each of a small lamellar 

 somewhat triangular body, furnished at its edge with a 

 number of long bristles, about twenty-four in number. 

 They are the " barbillons" of the mandibles, of Prevost 

 and Jurine. 



The thorax is cylindrical, and is composed of eleven 

 segments, each united to its fellow by a membrane, which 

 allows of a considerable degree of motion, permitting the 

 animal to curve its body in form of a circle, a position it 

 always seems to take when out of the water. The first 

 segment is the largest, the others gradually diminishing 

 in size as they descend. 



To each of these segments is attached a pair of branchial 

 feet (t. V, f. B.) These are broad and foliaceous, and 

 consist of three articulations. The first is the largest, 

 and has on its lower edge a semicircular branchial plate, 

 giving off about thirty or forty beautifully plumose hairs; 

 the second gives oif, on its inner edge, three square-shaped 

 projections, each of which sends off several long hairs ; 

 and the third is long and narrow, and gives off numerous 

 setae, also plumose, and of considerable length. From 

 the first joint, near its juncture with the second, there 

 arises a vesicle or flat body, which is studded over with 

 minute points, Ijut has no setae attached to it. It is of a 

 denser structure than the other portions. The first pair 

 of feet are the smallest, the others gradually increasing 

 in size till they reach the tenth pair, the eleventh being 

 considerably smaller than those preceding, though still 

 larger than the first. 



The abdomen is composed of nine segments, the two 

 first of which are the largest, the rest gradually diminish- 

 ing in size as they descend to the tail. This consists of 

 two lamellar appendages of considerable size, and beset 

 round the edges with numerous beautifully plumose 

 setae. 



Between the first and second segment of the abdomen 

 we see in the male the organs of generation, and in the 

 female the external ovary or oviferous pouch. The male 



