Among the bivalve mollusks, the oysters (Family Ostreidae) are rather specialized. Adult stages are sedentary and feed by straining the water for small food particles with the aid of a mucus sheet and a complicated and highly efficient ciliary mechanism. Oysters established their peculiar mode of life in Carboniferous times and have survived in large numbers ever since. Many diverse stocks, including peculiar forms and giant types flourished in ancient seas. Possibly a hundred or more species of three genera survive, living in depths from a thousand fathoms to above mean low tide in estuaries along the shores of all continents except Antarctica. The genus Pycnodonte is a purely marine or high salinity group, apparently relatively few in numbers, living from near surface levels to depths of 1000 fathoms. The shells have a peculiar cellular structure which permits tracing of the group to the distant past. The largest modern oysters belong to the genus Crassostrea. Oysters of this genus are estuarine and prolific; they form large reefs in many places, some of which rival coral reefs in area. Oysters of the genus Crassostrea usually flourish in the enclosed waters of bays, but under some circumstances they form reefs outside bays in shallow waters near large rivers, as on the coast of Louisiana. Embryonic and larval development takes place in the water entirely free of the parent. A large commercial production of Crassostrea virginica is centered in Louisiana and in Chesapeake Bay; the combined production of both is as great as...

Abstract Approximately 1,000 samples have been obtained from the bays of the centra! Texas coast. Their size parameters, constituents, and organisms have been studied in relation to salinity, depth of water, and relations to entering rivers and to inlets. All of these bays are cut off from free connection with the gulf by barrier islands, although widely-spaced inlets allow some exchange with gulf waters. Among the bay facies are (1) bays near stream mouths which have alternating silty clays and sands, commonly laminated and containing abundant plant fibers and aggregates, along with abundant ostracods in some localities; (2) shallow bays not related to stream mouths, which have an abundance of marine plants, a large number of gastropods, and higher sand content than most other bay environments; (3) deep central bays which have unstratified silty clay sediments commonly with a high content of benthonic Foraminifera in the coarse fraction; (4) central bays with oyster reefs which have been built up above the surrounding bay surfaces, and (5) bays near inlets or narrows where the currents have introduced considerable sand, and the sediment is a bimodal sandy clay with relatively small silt content. Borings into the bays and into the deltas recently built over their northern ends show that as much as 80 feet of bay sediment has accumulated during the past 9,000 years, since the ocean first came up into the valleys eroded during glacial stages, in what is now the bay area. The samples from the borings along most of San Antonio Bay show a remarkable constancy of sediment types with the only significant changes being from central bay facies to oyster-reef facies. The faunas, however, indicate salinity changes. No lamination and little stratification were found in the borings except near or under the delta at the head of the bay.