The dunes are relatively stabilized on the western side of the island, and there we found moderately dense stands of mesquite trees reaching heights of from eight to 10 feet. Prickly-pear cactus (_Opuntia lindheimeri_) was common in those stands of mesquite, and we saw an occasional yucca tree. A fairly dense ground cover was formed by blanket-flower (_Gaillardia pulchella_), marsh-elder (_Iva_ sp.), _Flaveria oppositifolia_, _Enstoma exaltatum_, and _Croton capitatus_ var. _albinoides_. A more open, xeric expression of the mesquite-cactus vegetation occurs on exposed, low clay dunes (see description by Price, 1933) located on alkaline flats bordering the laguna. At the time of our visit, most of the mesquites in these stands were dead or dying, the cactus was abundant, and the ground cover, which was sparse, included drop-seed (_Sporobolus virginicus_), ragweed (_Ambrosia psilostachya_), and _Commicarpus scandens_. On alkaline flats flooded by hypersaline waters of the laguna following heavy rains, _Batis maritima_ is found in the lower areas, but on the slightly elevated areas there is low and almost continuous cover of _Monanthochloë littoralis_, in which can be found _Batis_, _Borrichia fructescens_, _Salicornia_ sp., _Iva_ sp., and sea-lavender (_Limonium carolinianum_). Near Third Pass, sea oats (_Uniola paniculata_), evening primrose (_Oenothera_ sp.), and cordgrass (_Spartina_ sp.) are present on the dunes, and on alkaline flats we collected _Conocarpus erectus_, _Leucaena_ sp., and _Cassia fasciculata_ var. _ferrisiae_. Itinerary We reached Washington Beach from Matamoros on July 6, and drove to a point approximately 33 miles south on the beach, where we made Camp 1 on the east side of large dunes 400 yards from the surf. From this camp we worked the beach and dunes and also visited alkaline flats adjacent to the Laguna Madre. On the afternoon of July 8, we drove south along the beach and established Camp 2 on the south side of the Third Pass, approximately 73 miles south of Washington Beach. We had intended to go farther south but were unable to cross the Fourth Pass, an inlet three miles south of the Third Pass. We left the barrier island on the afternoon of July 10, after driving north from Camp 2 to the mouth of the Rio Grande, 11 miles north of Washington Beach. Mexican fishermen camped at the Fourth Pass told us that, had we been able to cross the Fourth Pass, it would have been possible to drive south on the beach all the way to La Pesca, a fishing village near the mouth of the Río Soto la Marina, approximately 150 miles south of Washington Beach. Summary of Previous Work in the Area The ornithologist H. E. Dresser (1865-1866) worked in southern Texas and at Matamoros, Tamaulipas, in 1863, and on one occasion reached the mouth of the Rio Grande ("Boca Grande"). He did not visit the barrier island or the Laguna Madre de Tamaulipas.