1927] Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo 279 
Avakubi in the Ituri River (Lang and Chapin Coll.) and in one of its 
affluents at the same locality (J. Bequaert Coll.). Stanleyville; Batama 
(Lang and Chapin Coll.). | | 
Specimens from Avakubi,, farther down the Ituri River than the 
type locality, agree perfectly with Thiele’s description and figure. When 
cleaned of their incrustation they are from bister to saccardo’s umber 
in color, sometimes lighter, ecru-olive in young specimens, glossy, with 
practically no minute sculpture except faint growth-lines. This separates 
it from P. mungwana, which is otherwise very similar. The spire of 
almost flat whorls tapers rather rapidly. The last whorl shows a very 
faintly traced, scarcely noticeable, peripheral angulation in adult shells, 
but distinct in young stages. The parietal callus is moderately strong, 
thickened posteriorly. 
: Length, 22.0 mm.; diameter, 11.0 mm.; length of aperture, 10.4 mm.; 3)4 whorls 
remaining. 
Length, 22.0 mm.; diameter, 10.6 mm.; length of aperture, 10.7 mm.; 2h 
whorls remaining. | 
Specimens from Stanleyville, where it was taken in abundance, 
are slightly more lengthened than those of the Ituri, generally showing 
a distinct angle on the penult whorl above the suture, and the spire tapers 
less rapidly. They have a black coat. The exact location was not noted, 
but they did not occur with any other large species. | 
Length, 23.0 mm.; diameter, 10.3 mm.; about 3 whorls remaining. 
BS ras “f OR woe Aa o 
Dupuis and Putzeys [1923, Ann. Soc. Zool. Belgique, LIII, (1922), 
pp. 77-78] have referred specimens from Stanleyville to P. lricincta, 
of which they claim P. ignobilis to be only a variety. Undoubtedly they 
examined the same species as here called zgnobilis. 
Potadoma pokoensis, new species 
Plate X XVI, Figures 12 and 12a 
Poko, from an affluent of the Bomokandi River (H. Lang Coll.); 
about 80 specimens. 
The shell is rather slender, somewhat thin, chestnut brown when the black coat 
is removed, rather glossy. Sculpture of about three spiral cords in the peripheral 
region of the last whorl and above the suture of the penult whorl, or part of it, not 
ascending further. On the spire a few rather indistinct spiral impressed lines are 
seen under the lens, with some indistinct and interrupted axial rugosity. The whorls 
are weakly convex, and in specimens seen only a few earliest ones are removed. 
The suture has a dark border on the upper whorls. The aperture is ovate; outer 
