OF THE EAST NORFOLK RIVERS. 437 
These are two marine Cyclopids which occur under the 
same conditions as the Calanoids above-mentioned. 
Thersites gasterostei, Pagenst. 
Except for Argulus foliaceus the fish of these rivers and 
Broads seem to me to be remarkably free from Crustacean 
parasites. The only other parasite that I have been able to 
find is Thersites gasterostei which is a peculiar little globular 
species living on the inner surface of the gill operculum of 
the Stickleback ( Gasterosteus acnleatus). Probably it is fairly 
common, since I have found it on nearly all of the few Stickle- 
backs caught. These few were taken in the Muckfleet and 
in the Yarc at Langley Dike. So far as I can find, this parasite 
has only once before been found in Great Britain, namely in 
Scotland. 
CIRRIPEDIA. 
B alan us improvisus, Darwin. 
In my list of 1903 I recorded a Balanus which I had not 
succeeded in naming. The specimens were subsequently 
submitted to Dr. Caiman who was good enough to identify 
them. Darwin, ' Monograph of the Balanida?,’ p. 252, 1854, 
states that it is a species of very wide distribution, taken 
occasionally in brackish water. In these rivers it is to be 
found in the adult condition on piles by the Muckfleet, the 
Yacht Quay at Yarmouth. Berney Arms and Oulton Broad. 
On the other hand, Nauplii probably belonging to this species 
are commonly found wherever the water is appreciably salt. 
It is curious that, in 1903, though the Nauplii were frequently 
found in Oulton Broad, not a single adult could be seen ; 
whereas, this year, they were there in abundance. 
COELENTERATA. 
Cordylophora lacustris, Allman. 
I have made some attempt this year to find out the exact 
range of this species of Hydroid in our rivers. In the Yare 
and Waveney I have not yet seen it at all. In the Bure it 
