The quahog or hard clam, Mercenaria mercenaria (Linne),2 which is widely distributed along the Atlantic Coast, is found in large enough numbers in the Chincoteague Bay area of Maryland to be economically important. Within this region, it is one of the most numerous and widespread species; yet its local abundance is highly variable. In 1953, the pattern of its distribution in the area was studied and analyzed for correlation with various environmental factors. Bottom type and current were studied in particular, with consideration of underwater vegetation, temperature, salinity, depth of water, and fishing pressure. The field work was done at the Chincoteague Bay Laboratory of the Maryland Department of Research and Education, located at Public Landing, Worcester County, under the direction of Mr. Fred W. Sieling.