A new diatom species, Tabellaria vetteri, is described from North-Central Pennsylvania. Unlike other representatives of the genus Tabellaria Ehrenberg, the new species lacks rimoportulae, the central part of its valve is internally thickened, and all girdle bands are open. Other characters, such as shape of the frustule, numerous ligulate girdle bands bearing septa, uniseriate striae with small poroid areolae, large apical pore fields, and simple spines fit the current concept of this genus. The new species is found so far only in two small soft-water streams and is especially abundant on sand.