1927] Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo 277 
little expanded and effuse at the junction of columellar and basal margins. Columella | 
concave, not heavily calloused. There is a thin, whitish or transparent callus on 
the penult whorl, slightly thickened near the posterior angle. 
Length, 33.0 mm.; diameter, 15.0 mm.; length of aperture, 13.7 mm.; 5 whorls 
remaining. 
Length, 33.7 mm.; diameter, 15.3 mm.; length of aperture, 15.0 mm.; about 
416 whorls remaining. 
This species differs from P. freethii (Gray), generally known as 
Melania nigritina Morelet, from the Gaboon, by the microscopic sculp- 
ture. That species is beautifully granulose, while in this the spiral striz, 
though waved a little, are not cut into granules (Fig. 46a). P. guineensis 
(Reeve) is stated by E. A. Smith to be “minutely granosely striated, 
but much more finely than in the type of M. freethii”’; thus also differ- 
ing from P. graptoconus. 
In one of the specimens from the Niari there are two dusky bands, 
a wider but indistinct one at the periphery and a narrower, more distinct 
band between that and the suture. 
— : 
Fig. 46. a, Potadoma graptoconus Pilsbry 
and Bequaert, and b, Potadoma schoutedent 
Pilsbry and Bequaert. Sculpture from suture 
to periphery of last whorl. xX 3. 
Potadoma schoutedeni, new species 
Plate XX, Figures 12 and 13 
Lukula (H. Schouteden Coll.). 
The shell is solid, with short, conic (truncate) spire, rounded periphery and 
tapering base; cinnamon-brown; not glossy; with very minute, close and distinct 
sculpture of spiral striee, of which there are 9 or 10 in one millimeter on the face of the 
last whorl (Fig. 46b). Near the columella there is a group of spiral cords, about 6 
in the type specimen. The whorls are but slightly convex up to the last, which 18 
quite convex in the peripheral region, and becomes a little inflated approaching the 
lip. The aperture is broadly ovate. . Outer lip is rather thick, sinuous, being retracted 
in the upper part, advancing below. The concave columellar margin is moderately 
calloused, and there is a rather strong parietal callus across the penult whorl, thickened 
into a callous pad near the posterior angle of the mouth. 
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