Studies on brackish water clams of the genus Rangia in Texas.

It has long been known that Rangia Cuneata and Rangia (Rangianella) flexuosa, though members of the marine family Mactridae, are rare in the saltier lower portions of bays and become more abundant in the upper portions (bay heads) where salinity is lowest and fluctuates most violently. Only recently has it been recognized that even the bay heads have salinities above the optimum for Rangia spp., and that R. cuneata, especially, attains its maximum abundance far up the river where the water is fresh more than half the time. R. flexuosa is less abundant than R. cuneata everywhere it occurs except in Clear Lake and perhaps in other lake estuaries on the west side of Galveston Bay. In Texas, R. cuneata is reported from the Nueces River, from Green Lake and Mission Lake (in the Guadalupe River delta), from the San Jacinto River, from the delta distributaries of the Trinity River, and from the Neches River and Sabine River, as well as from St. Charles Bay, Hynes Bay, Matagorda Bay, Lavaca Bay, upper Galveston Bay, Trinity Bay, East Bay and Sabine Lake (a lake estuary).