As to the geographical distribution, it should be briefly stated that the swollen forms (a_{3}) inhabit the largest rivers; the compressed forms (a_{1}) are found in the headwaters, and the intermediate forms (a_{2}) belong to the streams of moderate size. Intergrades are frequent. ANATOMY.[7] All these shells have the same, and an extremely characteristic and unique structure of the soft parts, so that there is not the slightest question that they belong together. I have examined the soft parts of some 200 specimens in the field, and over three dozens have been preserved in alcohol, and have been examined at leisure in the laboratory. They include representatives of the three main varieties, and of practically all of the individual variations. _Gravid females_ have been found on the following dates: May 11, ’13; May 15, ’13; May 16, ’13; May 20, ’13; May 20, ’14; May 22, ’14; May 25, ’14; July 5, ’13; July 9, ’13; July 10, ’13; July 13, ’13; July 14, ’13. _Glochidia_ have been observed on May 20, ’14 (immature), and July 14, ’13. Thus this species evidently is a summer breeder (tachytictic). The soft parts are those of the genus _Fusconaia_: the _supraanal_ is separated from the _anal_ by a very short mantle-connection, which is absent (or torn?) in rare cases. Inner lamina of inner gills free from abdominal sac. All four gills are marsupial. Placentae well developed and subcylindrical. _Branchial opening_ with well developed papillae, _anal_ with distinct, but small papillae. _Palpi_ subfalciform, posterior margins connected at base only. While thus the _Fusconaia_ structure is typically developed, this species is quite unique in its color. This concerns chiefly the color of the gonads, eggs, and placentae. The soft parts are often uniformly pale, whitish, but may shade to orange, and the orange is most prominent on foot, adductors, and mantle-margin; but the paler tints prevail, and often the orange is replaced by yellowish or brown. The gills are pale, but are generally suffused with blackish. The gonads are brown to red, mostly of a peculiar dull lavender color in the female, and the latter color, or purplish brown, is the prevailing color of the eggs and placentae. The charged gills become thus rather dark purple, or purple-brown, shading sometimes to dull red or blackish, in other cases to brownish, brownish pink, brick-red, or even pale brown. These are very peculiar tints, by which this species is easily recognized in the field: four marsupial gills of this blackish-purple color are not known in any other Nayad. _Glochidia_ have been found only in specimens belonging to the headwaters variety (_barnesiana bigbyensis_). They are subelliptical, slightly higher than long, L. 0.15, H. 0.16 mm.