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 off, 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, but 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 
