Length of first sixteen segments, 15 mm.; including branchiæ, 21 mm.; width, 2.5 mm. Type--M. C. Z. 2, 172. _Potamilla colorata_ sp. nov. The type is notably marked with black pigment; the collar membrane crossed with a close series of longitudinal dark stripes, one in line with each radiole and narrowing caudad; the branchiæ crossed transversely with dark bands. Thoracic somites, more notably the anterior ones, with a dusky to black band in front of each uncinigerous torus and a dark spot on the dorsum mesad of the setigerous papilla. The collar with a dark area ventrad and also dorsad of the fascicle. Ground color greyish of light brown cast, lacking the yellow dominating in omissa. Sixteen (or seventeen) pairs of radioles in the branchiæ. Ventral lobes of collar pointed, widely overlapping in the median line, dorsal ends free, projecting toward each other in dorsal groove. Setigerous thoracic somites eight in number. Inferior setæ numerous, spatulate, usually in two series. Total number of segments present about fifty-one, a few of the most caudal being lost. Length, 25 mm.; with branchiæ, 30 mm. Type--M. C. Z. 2, 173. _Pseudopotamilla paurops_ sp. nov. A rather slender species with branchiæ of moderate length. Excepting the eyes with no pigmented markings. Radioles fifteen pairs. Eyes few, not present on all radioles; where present usually but a single one on each radiole, in one case two; the eyes deep purple, variable in side from moderate to small; situated at varying distance between base and middle of length of radioles. Free dorsal edge of branchial membrane with two short obtuse lobes overlapping in the middle line. The dorsal notch in the collar lobe on each side is mesad of the line of setigerous tubercles, wide open, rectangular or slightly obtuse; lobe mesad of notch small, anteriorly rounded, the mesal edge extending into the dorsal furrow; median ventral lobes separated by a narrow incision, short, the ectal edge passing out in an even concave curve to the anterior lateral margin. A characteristic feature of the species is the presence of ten setigerous thoracic somites. Dorsal setæ of the usual two types of which the upper are much fewer spatulate setæ in two series with distal expansion broad and wings asymmetrical, tip short. Total number of segments, seventy-eight. Length without branchiæ, 31 mm.; with branchiæ, 36 mm. Type--M. C. Z. 2, 174. Tube tough, corneus. _Pseudopotamilla parva_ sp. nov.