The spawning cycles of two potentially valuable commercial shellfish species in Massachusetts were examined to determine timing of gametogenic development. The “southern” surfclam , Spisula solidissima similis , is a subspecies of Spisula solidissima solidissima, the commercially harvested Atlantic surfclam , and has been experimentally grown in Massachusetts coastal waters with recent success. The intertidal fishery for the razor clam, Ensis directus , has become increasingly important in areas of Massachusetts, but little is known of the seasonal reproductive patterns of either species. To address this question in local populations, a sample of 10 clams of each species was examined at monthly intervals over two years. Morphometric data (shell length, weight) was collected before each clam was opened to visually determine gonadal development. A gonad tissue sample was then examined under a microscope to determine the presence/absence of germ cells, and to estimate the developmental stage. Preliminary results suggest that E. directus in Cape Cod Bay spawn in May, similar to documented spawning times of populations in northern Europe and Canada and aligning with seasonal water temperature increases. S. s. similis appear to spawn in late May-June, later than southern populations but also reflecting the spring warming of water temperatures in the northern latitudinal region. Both species exhibited an additional spawn in September, an occurrence potentially driven by food availability as well as water temperature. While peak spawning typically occurs in the spring, with a warming climate and oceans, and a subsequently longer growing season, fall spawns could become more prevalent in New England species.