26 Messrs. G. S. Brady and D. Robertson on the 
the height; posterior margin indented in the middle at the 
junction of the two valves: end view nearly circular. Shell 
of the male somewhat more compressed, when seen from 
above, having the greatest width near the middle. The 
right valve much overlaps the left, especially in the middle 
of the ventral margin. Superos antenne excessively short 
and stout, the joints much broader than long, except the 
last two and tlie first, whose breadth and length are nearly 
equal ; all the joints except the first armed with very strong 
curved sete, the longer of which are nearly equal in length 
to the last five joints of the antennz, the shorter equal to 
the last two joints. Inferior antennas also very short and 
stout; terminal claws nearly straight, with upturned extre- 
mities ; ; last joint very short, with two stout, equal, apical 
spines ; penultimate with three apical spines of equal length 
and one short seta, antepenultimate with one long and one 
rather shorter seta ; [RE joint thicker, having two slender 
sete rising from independent bases. Joints of the second 
and third feet gama serene in length from the first 
to the last; the longer e two terminal claws equal in 
length to the three cius joints ; second and third joints 
armed on the posterior margins with several short sha 
sete or prickles. The shell is me or milk-white, often 
slightly granular in appearance, and showing through it 
the limbs of the EE e as well as the ova and fully deve- 
loped young. The infero-posteal angle of the shell is eet 
with a dense tuft of microscopie beaded hairs (fig. 14). 
Length 4*4 inch. 
Hab. ittlesea Dyke, and on the site of Whittlesea Mere ; 
the rivers Nene, Cam, Ouse, Deben, and Scheldt ; Lake 
Lothing and Breydon "Water; and the broads of Wrox- 
ham, Jarton, Horsey, Hickling, Somerton, Ormesby, and 
Oulton. 
A most extensively distributed and abundant species through- 
out the East-Anglian district, the only gathering in which we 
failed to find it being that from the river Bure, which it may 
be said was made under very unfavourable circumstances. 
Except in the river Scheldt, P. Stevensoni pee not yet been 
found outside of this district, where its t abundance in 
objects of our visit to the d we are indebted for much o 
our success. 
