1927] Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo = 287 
nearly as early as the two primary keels, so that three show on the whole 
penult whorl. In still other examples this intermediate keel is wanting 
throughout. 7 
Potadoma superba mut. inculta, new mutation 
Plate XXV, Figures 5 and 5a 
With the typical form in the Tshopo River at Stanleyville (H. Lang 
and J. Bequaert Coll.). 
As in P. ponthiervillensis, there is also a nearly smooth form which may be 
designated mutation inculta. None of the specimens attain so large a size as some of 
the typicalform. The early whorls are as described for the type; the last two become 
more convex, and show very weak traces of several spiral cords, of which that girding 
the periphery is most developed, and in some examples the only one. 
Length, 37.0 mm.; diameter, 16 mm.; 34 whorls remaining. Type. 
aaa cua 4 
66 28.0 66 13 2M 5 a 
fe 24.0 66 10 3h5 ce 66 
This form differs from P. mungwana by the strongly convex last 
whorl, the more conic contour and larger size. 
Potadoma mungwana, new species 
Plate XXV, Figure 4 
Tshopo River near Stanleyville (H. Lang Coll.). 
The shell is solid, slowly tapering, approaching a subcylindric contour, the last 
whorl having a peripheral angle (usually rather indistinct), the whorls but slightly 
convex. Surface somewhat glossy, smooth to the eye, but under a lens showing fine 
sculpture of irregular axial wrinkles cut by weakly incised spiral lines, forming where 
best developed a distinctly decussate pattern; over this there is more or less minute, 
irregularly developed rugosity or granulation. The color is carob brown or somewhat 
darker. The aperture is ovate, somewhat produced at the base. Outer lip thin, very 
slightly sinuous. Columella but little thickened. Parietal callus thin in the middle, 
thickened to form a low tubercle or callous pad near the upper insertion. 
~ Length, 24.5 mm.; diameter, 9.8 mm.; length of aperture, 10.3 mm.; 345 whorls 
remaining. Type. 
This species differs from P. alutacea and P. ignobilis in the minute 
sculpture. In general appearance these three species are much alike. 
The minute sculpture of P. mungwana is the same as in immature P. 
superba and P. superba inculta; these species diverge in their later stages 
of growth. 
