Land and Fresh-Water Crustacea around Edinburgh. 363 
within the post-Tertiary period, why is it at present found 
only in the south and west of England, and is scarce even in 
these localities? If the Apus remains found by Mr Bennie 
belong to Apus glacialis, and there is reason to believe that 
they do, the reason why Apuws was common in the 
post-Tertiary lake at Corstorphine, but is not known 
to occur anywhere in Scotland now, is not difficult to 
explain. <Apus glacialis is a dweller in regions where an 
arctic or subarctic climate prevails, so, when the rigorous 
climate of our country, during the early portion of the post- 
Tertiary period, became gradually more and more temperate, 
Apus glacialis died out, just as Pecten islandicus, once so 
common in our seas, and the shells of which are so plentiful — 
in some of the laminated clays of the west of Scotland, dis- 
appeared, and is only now found living in high latitudes. Mr 
Bennie discovered the remains of boreal plants in the same 
deposit with those Apus, and this strengthens still more — 
the supposition that the fragments from the Corstorphine 
lake-deposit are those of the northern Apus. Apus canert- 
formis, on the other hand, has apparently a more southern 
distribution, which may account for it, also, not being found 
in Scotland. Though it is thus almost certain that no 
Phyllopods now exist in our district, I should not be sur- 
prised if Argulus foliaceus—the British representative of the 
Branchiura—may yet be found to be a member of the district 
fauna. -Argulus is a parasite on various fresh-water fishes, 
as the trout, pike, carp, stickleback, etc. It is very depressed 
and round, and only about the one-fifth of an inch across, and 
as it sticks close on the skin of the fish, it may be easily 
overlooked. -Argulus can swim freely when it chooses to do 
so, and may then be caught by tow-net, but usually it is 
obtained adhering to fish. 
The Cladocera obtained in the district around Edinburgh 
number twenty-nine species, and belong to twenty-two 
genera. In the following list the arrangement and nomen- 
clature of C. L. Herrick’s “ Final Report on the Crustacea of 
Minnesota” is more or less adhered to. Dr Baird’s classical 
work on the British Entomostraca, and the “ Monograph of 
the British Entomostraca belonging to the families Bosminide, 
"Ve F gc P4: 
