At the time of our visit, the part of the barrier beach south of the tidal inlet was connected with the mainland. The connection was far to the southward, according to our pilot, Mr. Kagy of Brownsville, and also according to the testimony of the Mexicans at the fishing camp where we stayed on the north side of the inlet. The barrier beach which lay to the north of the inlet extended sixty-odd miles northward to the delta of the Rio Grande and had, we were told, eight "passes," including Paso Jesus Maria. At the time of our visit, however, only three of these tidal inlets were open, it was said; the five others were thought to be filled in with sand, which permitted terrestrial animals to move from one part of the beach to another. Dr. von Wedel and I saw two tidal inlets that were open when we were being flown back to Brownsville. [Illustration: FIG. 1. Diagram of physiographic features of the barrier beach of Tamaulipas. Top view looking down, as from an airplane, on the beach. Bottom view is profile.] The long, low, sandy island, technically a barrier beach, irrespective of tide varied in width from a quarter of a mile to as much as a mile and was separated from the mainland by the Laguna Madre, which was four miles wide opposite our trapping station. To the northward the width of the lagoon gradually increased until, at a place thirty miles north of our trapping station, the lagoon was almost 20 miles wide. The island was perhaps four feet above high tide. Superimposed on this, in places, there were sand dunes, technically barchans, so arranged that the end of one touched the end of the next. The tops of some were as much as 20 feet above high tides and the chain of these connected-dunes on which we trapped was approximately a mile long. Incipient tidal inlets were frequent; they were where storm-driven waves of high tides had broken across the island between the adjacent ends of two dunes. The windward side of a dune was toward the Gulf and the slope of that side was gentler than that on the leeward side. According to the cycle described by Davis (Proc. Amer. Acad. Arts and Sciences, 22:303-332, 1896) and recently figured on page 364 by Lobeck (Geomorphology, 1st ed., xii + 731 pp., 1939, McGraw Hill Book Co., Inc., New York) the barrier beach concerned was in the early part of the "Middle Youth Stage". Typically, on the center of the area in the lee of a dune there was a patch of plum brush, almost five feet tall and so dense that a person could not penetrate it. A belt of grass, 20 to 100 feet wide, surrounded the plum brush. The grass was approximately 20 inches high. Outside the area of grass, there were widely-spaced xerophitic shrubs which grew also on the dunes. The diagram (fig. 1) shows these prominent features as a person might see them if he looked directly down from an airplane.