GAMMARUS PULEX. 
391 
published by Loven.* These two inland fresh-water 
lakes are situated on high ground, and have the surface 
of their waters three hundred feet above the level of the 
Baltic, whereas the bottom is one hundred and twenty 
feet below such level. In these lakes (which appear to have 
been lifted up with the gradual uprising of the country) 
have been found several genera and species of Crustacea, 
three of which are Amphipoda, which are affirmed to be 
identical with marine ones, namely, Gammar acanthus 
loricatus (Sabine, Ross, Kroyer), Pontoporeia affinis (Lind- 
strom),*f and Gammarus cancelloides (Gerstfeldt) J. The first 
is now only known to exist in the Arctic seas, the second 
in the Baltic, and the last was found in Lake Baikal, 
in Central Asia. It is therefore suggested by Loven that 
when the land was raised so as to convert these waters 
from marine bays into inland lakes, these marine species 
were retained within the basins, the waters of which have 
since been changed, through the agency of springs, into 
fresh- water; and with the gradual transfer of the water the 
habits of the animals have also changed gradually, and 
that without any outward alteration of form. Prof. Loven 
thinks that there is sufficient evidence to show that this 
change in the conditions of these lakes must have taken 
place during the great glacial period, at a time when the 
* Ofvers. af Kongl. Yet. Akad. 1861, No. 6. 
f Ofvers. af Kongl. Yet. Akad. Forhandl. 1855, p. 68. 
X Gerstfeldt, Mem. de l’Acad. de St. Petersburg, viii. pp. 287-8, ix. tab. 
fig. 8. 
Through the kindness of Professor Kinahan, who received them from 
Prof. Loven, we have had an opportunity of examining specimens of these 
three amphipoda, and, certainly, except in their being of smaller dimensions, 
we can perceive no distinction between them and the marine specimens. 
With the Siberian G. cancelloides, Gerstfeldt, we are not acquainted, but 
observe that the specimen from Sweden is not a Gammarus, and that it bears 
no very distant resemblance to Pallasea cancellus (Pallas). Besides the 
above, the following marine Crustacea have been taken in these fresh-water 
lakes, Mysis relicta , N.S., and Idolhea entomon , L. 
