ZOOLOGY OF HYLTON DENE. 97 
differences. Those of the first and most saline group are marked 
chiefly by the presence, during the autumn months, in con- 
siderable abundance, of two nudibranchiate molluses, Alderia 
modesta and Limapontia depressa. They contain also in common 
with the second group various crustacea, Gammarus locusta, 
Orchestia littorea, Palemon varians, Crangon vulgaris, Corophium 
longicorne, Spheroma (? rugicauda) and Temora velox, an Ento- 
mostracan of the order Calanide. Besides these there are two 
or three species of Foraminifera, and some Annelida, I think of 
the genus Nereis. The second group is characterized more by 
the absence of certain species which occur in the first and third, 
than by any inhabitants peculiar to itself, though there are one 
or two animals of no special interest which I have found only 
here. The large pool which forms our third division differs in 
nothing excepting its peeuliar Crustacean fauna from an ordi- 
nary fresh water pond. It lies outside the boundary line of the 
Wear Commissioners, and is not therefore affected by river floods. 
‘It is of tolerable depth, but very narrow, more like a tortuous 
ditch than a pond; and it affords a home to numerous Notonecte, 
Beetles, Water-rats, to a few individuals, small and stunted, of 
Limneus pereger and to a beautiful Polyzoon—Plumatella repens: 
The Entomostraca of this pool are all purely fresh water spe- 
cies, such as Cyclops quadricornis, Candona lucens, and several 
Cyprides. The most interesting inhabitants are, however, some 
of the larger Crustacea, Palemon varians, Mysis vulgaris and 
Corophium long:corne, all of which occur in great numbers. I 
know of no other instance where any of these occur in absolutely 
fresh water, and their association with such undoubted fresh 
water species as those mentioned above seems to me a matter of 
very great interest. It is strange to see Prawns and Shrimps 
gliding among the leaves of Callitriche and overshadowed by 
blossoming wild rose and whin. It is remarkable that these Crus- 
tacea seem to have undergone no deterioration from their residence 
in fresh water; the specimens taken there are quite as fine as 
those which we meet with in salt water localities, except per- 
haps in the case of Corophium, which is rather small, and of 
which there is an unusual preponderance of females. It is 
