[3] There are a great many instances of discontinuous distribution among Oriental Invertebrates. Thus the Freshwater Crab (_Thelphusa fluviatilis_) occurs in Southern Italy, Greece, Turkey, Cyprus, and Asia Minor. Another crustacean--a Freshwater Crayfish--(_Hemicaridina Desmaresti_) inhabits Spain, Corsica, Sardinia, Sicily, and Asia Minor. CHAPTER VII. THE LUSITANIAN FAUNA. Under the Roman Emperor Augustus, the Spanish peninsula was divided into three provinces, one of which--namely Lusitania--occupied a large portion of the present area of Portugal. The term "Lusitanian" is therefore almost synonymous with Portuguese, but it has frequently been applied by zoologists and botanists in a much wider sense, so as to vaguely include the extreme south-west of Europe without any definite limits. Neither do I propose to restrict the term to everything found within the borders of Portugal. For the sake of convenience, we may designate as Lusitanian forms those animals and plants which have migrated to Central, Southern, or Northern Europe from South-western Europe. They may really be North-west African species, or they may have originated on land which lay to the west of Portugal, and which is now mostly buried beneath a deep sea. Nevertheless, we have received them from the extreme south-western portion of our continent--they have come to greater Europe from that direction. In discussing the component elements of the British fauna and flora in the third chapter, I have already referred to the distinguishing characters of the Lusitanian migrants and to their distribution. I need only repeat, therefore, that these are now principally confined to the south-western portions of the British Islands. The late Edward Forbes was the first to trace the Lusitanian flora to its native home. In his classical memoir on the geological relations of the existing fauna and flora of the British Isles, he laid the foundations of a new method of research. We are as yet only beginning to realise the far-reaching conclusions obtainable by a careful study of the geographical distribution of animals and plants, though the lines of investigation were indicated by him more than fifty years ago. Forbes was of opinion that the Lusitanian element in the British flora was of miocene age, and that it survived the Glacial period on a now sunken land to the south-west of Ireland. Mr. Carpenter and myself agree in so far that we are both inclined to look upon this Lusitanian flora and the accompanying fauna in Ireland as of pre-glacial origin. But I am not quite satisfied that the Lusitanian migration ceased to come north then. It may have received a temporary check; but the presence, for instance, of the Dartford Warbler (_Melizophilus undatus_) in the south-east of England would seem to indicate that its northward migration took place in very recent times. It is possible also that the very restricted occurrence of the Dartford Warbler may imply that it is gradually