through the East Indies and found also in the Mediterranean. The former channel, if one ever existed, had, therefore, much the same value in distribution of species as the present Suez Canal. =Geological Evidence of Submergence of the Isthmus of Suez.=--Yet, from geological data, there is strong evidence that the Isthmus of Suez was submerged in relatively recent times. The recognized geological maps of the Isthmus show that a broad area of post-Pliocene or Pliocene deposits constitutes the Isthmus and separates the nummulitic hills of Suez from their fellows about thirty miles to the eastward. The northern part of the Isthmus is alluvium from the Nile, and its western part is covered with drifting sands. The Red Sea once extended farther north than now and the Mediterranean farther to the southeast. Assuming the maps to be correct, the Isthmus must have been open water in the late Pliocene or post-Pliocene times. Admitting this as a fact, the difference in the fish fauna would seem to show that the waters over the submerged area were so shallow that the rock-loving forms did not and could not cross it. Moreover, the region was very likely overspread with silt-bearing fresh waters from the Nile. To such fishes as _Chætodon_, _Holocentrus_, _Thalassoma_ of the Red Sea, or to _Crenilabrus_, _Boops_, and _Zeus_ of the Mediterranean, such waters would form a barrier as effective as the sand-dunes of to-day. =Conclusions as to the Isthmus of Suez.=--We are led, therefore, to these conclusions: 1. There is no evidence derivable from the fishes of the recent submergence of the Isthmus of Suez. 2. If the Isthmus was submerged in Pliocene or post-Pliocene times, the resultant channel was shallow and muddy, so that ordinary marine fishes or fishes of rock bottoms or of deep waters did not cross it. 3. It formed an open water to brackish-water fishes only. 4. The types common to Japan and the Mediterranean did not enter either region from the other by way of the Red Sea. 5. As most of these are found also in India or Australia or both, their dispersion was probably around the south coast of Africa or by the Cape of Good Hope. 6. In view of the fact that numerous East Indian genera, as _Zanclus_, _Enoplosus_, _Toxotes_, _Ephippus_, _Platax_, _Teuthis_, _Acanthurus_ (_Monoceros_), _Myripristis_ occur in the Eocene rocks of Tuscany, Syria, and Switzerland, we may well suppose that an open waterway across Africa then existed. Perhaps these forms were destroyed in European waters by a wave of glacial cold, perhaps after the Miocene. As our knowledge of the Miocene fish faunæ of Europe is still imperfect, we cannot locate accurately the period of their disappearance. About half the species found in the Eocene of Italy belong to existing genera, and these genera are almost all now represented in the Indian fauna, and those named above with others are confined to it.