650 MR. R. GURNEY ON FRESH- AND BRACKISH-WATER CRUSTACEA. 
found in quite fresh water, it occurs in abundance 
in Hickling, Horsey Mere, Heigham Sounds, and 
Martham Broad, and doubtless in parts of the 
Thurne also, though I have not searched for it 
there. The explanation of its presence in Broads, 
so far from the reach of the tides, is to be found 
in the probable existence of salt springs in Horsey 
Mere. The salinity of the water in Horsey Mere 
may reach as high as 112 grains of Chlorine per 
gallon, and it is also very high in the other Broads 
mentioned. The water of the Thurne west of 
Potter Heigham is normally too fresh for Neomysis 
to be able to live in it, so that in the Hickling 
region Neomysis is practically shut off from the 
river Bure. At periods of exceptionally high tides, 
however, it would be possible for it to run up from 
the Bure, and in this way establish itself in the 
more or less salt Broads higher up. At such times 
it does actually extend far beyond its usual range ; 
in fact, I have even taken it on one occasion at 
Ludham Bridge. 
Isopod A. 
Heterotanais, sp. (?). I have taken specimens at Six-mile House 
on the Bure, and at Reedham in the Yare, of an 
Isopod which appears to belong to the genus 
Heterotanais, but which does not agree with any 
species which I can find described. 
Gnathia maxillaris (Montague). This species is commonly found 
in the Norfolk rivers, on the borderland between 
fresh and salt water ; the only Broad in which it 
occurs is Oulton. 
Sph^eroma serratum (Fabr.). Distribution as for the preceding 
species except that it has also been taken in 
Rockland Broad. 
Ligia oceanica (Linn.). Has been found by my brother, Mr. 
Eustace Gurney, at Reedham, and by myself in 
a tank of fresh water standing by the river Yare at 
Berney Arms, and containing Daphnia pulex. 
Asellus aquaticus (Linn.). Common everywhere. 
