5A BRITISH COPEPODA. 
a vesiculiform swelling, the last jomt hooked. Acces- 
sory branch of posterior antenna (fig. 15) very small, 
biarticulate ; mandible-palp (fig. 16) small, biarticulate, 
unbranched, and bearing four small sete. First foot- 
jaw (fig. 17) divided into four setiferous segments ; 
second small (fig. 18) and forming a clawed hand. 
The first four pairs of feet have both branches 3- 
jointed ; the inner branch of the first pair (fig. 19) is 
rather longer than the outer, its first joint beg as 
long as the second and third together, and having a 
long seta and three or four small hairs on its inner 
margin ; the inner branches of the second, third, and 
fourth pairs are considerably longer than the outer, 
and the outer margins of all are fringed with spine- 
like hairs; the third and fourth pairs longer than the 
first two. Fifth pair in the female (fig 21) 2-joimted, 
the basal joint short and broad, its inner segment 
fringed with three short, equal spines, and two longer 
ones, besides numerous short hairs; the second joint is 
sub-ovate, fringed with fine hairs and having five long 
apical sete. In the male (fig. 22) the fifth pair is 
obsolete, being reduced to a minute setiferous lobe. 
Caudal segments very short, bearing two principal 
sete, the outer half as long as theinner. Length 34th 
of an inch (9 mm ). 
This is a brackish-water species inhabiting the same 
sort of localities as Tachidius brevicornis, from which, 
however, it 1s perfectly distinct. I have taken it in a 
large pond, subject to occasional tidal influx, at St. 
Mary’s (Scilly); in brackish pools by the River Stour, 
at Manningtree, and in Oulton Broad (Suffolk) ; it 
