It has been long known that certain marine fishes enter fresh-water in addition to anadromous species that run up rivers to spawn. Gunther (1880, p. 202) said: Almost every large river offers instances of truly marine fishes ascending for hundreds of miles of their course; and not periodically,, or from any apparent physiological necessity, but sporadically throughout the year . Ordinary faunistic surveys, which are usually made without salinity determinations, indicate that this phenomenon is more common in the tropics than in temperate regions. Nevertheless, it is common in North America and several authors have mentioned it. Marine fishes are found in the Atchafalaya River of Louisiana over 160 miles from the sea (Gunter, 1938b) and numerous marine species occur in fresh-water at Homasassa Springs, Florida (Gunter, 1942, Herald and Strickland, 1949). Bailey, Winn and Smith (1954) qttestioned these records but furnished others for the Gulf Coast. Odum (1953) has shown that the fresh-waters of Florida generally, including Homosassa Springs are quite high in salt content. Crabs (Gunter, 1938b) and other marine animals also enter fresh-water, but the action is much more common to fishes and doubtless takes place at all coastal river mouths to some extent. Some fresh-water fishes also descend the rivers and spend a time at sea. Myers (1938, 1949) has proposed a six division classification of fishes with regard to salt tolerance, which is particularly useful in zoogeographic studies. In this paper we are not particularly concerned with those problems. Remarks and records in the literature on the salinity where fishes are captured are scattered, incomplete and hard to find because they are included as side issues in papers devoted to other subjects. The writer attempted to summarize the information for North and Middle America by compiling a list of the fishes of the continent which have been found in both freshwater and sea water (Gunter, 1942). Due to the incompleteness of the literature, the help of a number of ichthyological workers was solicited. The response was gratifying and several unrecorded observations were brought to light. This paper is essentially a revision and extension of the former list. An animal which will withstand or tolerate gross salinity changes is said to be euryhalin. There are all degrees of euryhalinity, grading from animals which can withstand little or no salinity change to those which can change from sea water to fresh-water or vice versa and live in either environment indefinitely. There are also degrees of rapidity withwhich animals can undergo salinity changes, but little is known of this aspect of the subject. The term euryhalin has never been rigidly defined and any rigid definition is essentially arbitrary. The writer (Gunter, op. cit.) defined an euryhalin