Geographical Distribution of Phreatoicus

Abstract

THE occurrence of the isopod Phreatoicus in a fresh-water stream near Cape Town, in South Africa, as recorded in your issue of June 12 by Mr. Keppel H. Barnard, is of very considerable interest from the point of view of the geographical distribution of the group. Since I described the first species of the genus in 1884 our knowledge of this group has grown very rapidly, and there are now known three species of Phreatoicus in New Zealand, two subterranean and one from surface waters, and several species grouped under allied genera from Australia and Tasmania. The genus is shown both by its generalised character and by its distribution to be an ancient one. I have long considered that it is probably a fresh-water form that has developed in subantarctic lands, and its discovery in South Africa seems to confirm this. In New Zealand it appears to be confined to the more southerly portion, but it was not found in the subantarctic islands to the south of New Zealand when these were visited in 1907. It should, however, be looked for in other subantarctic islands, particularly St. Paul and Amsterdam Islands in the Indian Ocean, and the Falkland Islands and adjoining parts of South America.