To the same group of animals also belong the three remarkable species of freshwater sponges, _Ephydatia crateriformis_, _Heteromeyenia Ryderi_, and _Tubella pensylvanica_, which Dr. Hanitsch has described from some lakes in Western Ireland. None of these are known from Great Britain or from the continent of Europe. A few North American plants grow wild in the same district. That any of these should owe their existence in Ireland to accidental introduction appears to me exceedingly improbable. In a former contribution to this subject (_a_, p. 475) I assumed that these American plants and animals had migrated to Europe at the same time as the other northern forms referred to. My friend Mr. Carpenter, however, takes exception to this (p. 383), and I quite recognise the force of his argument. "Their very restricted and discontinuous ranges," he says, "along the extreme western margin of Europe mark them as decidedly older than those northern animals and plants which have a circumpolar distribution." We have indeed quite similar examples in the Oriental migration, of which part is very ancient, surviving here and there and exhibiting discontinuous distribution. We may therefore look upon these American immigrants as among the oldest members of that northern stock which have survived in our islands--probably a mere remnant of a once luxuriant flora and fauna. In order to show the importance of the Eastern or Siberian element in the English, or, we might say with Dr. Sclater, the Anglo-Scotian mammalian fauna, I herewith give a list of the species of mammals which probably migrated to Great Britain from Siberia. I have marked with an asterisk those which still exist in this country (not in Ireland), or have become extinct within historic times. Canis lagopus. Gulo luscus. * Mustela erminea. * " putorius. * " vulgaris. * Sorex vulgaris. Lagomys pusillus. * Castor fiber. Spermophilus Eversmanni. " erythrogenoides. * Mus minutus. * Arvicola agrestis. * " amphibius. " arvalis. * " glareolus. " gregalis. " ratticeps. Equus caballus. Saiga tartarica. Ovibos moschatus. Cricetus songarus. Myodes lemmus. Cuniculus torquatus. Alces latifrons. " machlis. Rangifer tarandus.