We observed six diatom taxa from North American samples and one taxon from China that are considered within the genus Encyonema Ktzing. Two of the taxa are described as new, Encyonema reimeri Spaulding, Pool et Castro sp. nov. and Encyonema nicafei Spaulding sp. nov. A third taxon, Encyonema stoermeri Spaulding, Pool et Castro nom. nov., shat. nov. is assigned a new name and rank. In the past, these taxa have been ascribed to several names, but primarily the names Cymbella muelleri Hustedt and C. muelleri f. ventricosa (Tempre et Peragallo) Reimer have been used, based on their inclusion in the two volumes of "The Diatoms of the United States". We compare the new species with other members of this group of taxa, including Encyonema latum Krammer, E. sinicum Krammer and E. yellowstonianum Krammer. This group of species shares the features of 1) a broad axial area, 2) raphe branches curved with the convex side toward the dorsal valve margin, 3) slightly expanded and dorsally deflected proximal raphe ends, and 4) oval areolae near the axial area, becoming lineolate, or transapically elongate, towards the dorsal margin. We expect that many of the species reported in the U.S. have been identified using names of species from other continents. We also expect that critical microscopy and use of original literature is likely to clarify the geographic distribution of species within Encyonema. This work is important in order to understand, document and protect the species diversity of diatoms and their aquatic habitats.