OF THE EAST NORFOLK RIVERS. 427 
specimens carried down with the stream into water too salt 
for them. 
The presence of several marine Malacostraca in water in 
which a fresh-water fauna was able to maintain itself is 
rather remarkable. The species referred to are Coremapus 
versiculatus, Corophiwn grossipes, Hderotanais gurneyi and 
Cyatkura carinata, all sedentary or burrowing species. They 
are found in mud and under bark on some piles supporting the 
bank nearly opposite the Muckfleet Dike. In this position, 
where are also to be found Balanus improvisus and Nereis 
diversicolor, they are exposed to great changes of salinity, 
and, during some seasons, cannot be reached by really salt 
water for very long periods. Of course one cannot say, from 
the presence of any species in a living state, how long it has 
been in that place or how long it can remain, but there is no 
such doubt in the case of Balanus, and there is good reason 
to believe that the other species were really established in 
their position. 
The truly brackish-water species, or those which range on 
the one hand into fresh water and on the other into salt 
are the following : — 
Balanus improvisus, Darwin. 
Tachidius littoralis, Poppe. 
,, discipes, Giesb. 
Laophonte mohammed, Blanch and Rich. 
Nannopus palustris, Brady. 
Cyclops lubbockii, Brady. 
,, .equoreus, Fischer. 
Eurytemora affinis, Poppe. 
Gammarus duebeni, Lillj. 
Melita pellucida, Sars. 
Coremapus versiculatus (Bate). 
Corophium grossipes (Linn). 
Heterotanais gurneyi, Norman. 
Cyathura carinata, Kroyer. 
Gnathia maxillaris (Mont.). 
Neomysis vulgaris (Thomps.). 
Pal.emonetes varians (Leach). 
f f 2 
