OF THE EAST NORFOLK RIVERS. 
433 
while giving some illustrations of it here, owing to its interest 
as a species new to Britain. It is readily distinguished 
from Anthura gracilis (Mont.), by the rounded form of 
the telson, the very much larger opercular appendages and 
by the form of the antennae. My specimens do not show 
distinctly the ventral keel from which the species takes its 
name. 
I believe that this is the species referred to under the name 
of Anthura gracilis by Milne Edwards,* and not Paranthura 
nigropunctata (Lucas), as suggested by Norman and Stebbing. 
Thienemann also.f in describing statocysts in the tail of 
Anthura gracilis was evidently dealing with Cyalhura carinata. 
His specimens and those of Kuhlgat/ were taken in the Baltic 
in brackish water in the mouths of rivers. 
I have found specimens of this species in three localities, 
namely on piles by the Muckfleet and at Acle Bridge (Bure), 
and at Oulton Broad, but it seems to be rare, and altogether 
I have only taken 5 female specimens. On the other hand, 
it may not be so rare as it seems, since it requires very careful 
search to find it. Its habit is to burrow in the fine mud which 
collects behind the bark of posts driven into the river bottom, 
or under stones, and it seems to be capable of living in water 
either fresh or brackish. At Oulton Broad, at the time of 
capture, the water was very salt, but on the three other 
occasions on which it has been met with the water in which 
it was living was practically fresh. 
Sph.eroma rugicauda, Leach. 
In my list I gave only S. serration , Leach, but it seems 
probable that I may have sometimes confused the two species, 
since the young of S. serration are not at all easy to separate 
from S. rugicauda. Actually, the latter seems to be the com- 
moner. Both may be met with together, but neither occur 
in water that is not of a very high salinity. J Both are com- 
monly found under stones, and on Enteromorpha. 
* Hist. Nat. ties Crustaces. iii. p. 136. 
t Zool. Anz. xxvi. 1902, p. 406. 
X The record given of the occurrence of S. serratum (1903, p. 650) in 
Rockland Broad is a remarkable exception. 
