é 
1927] Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo 285 
axial wrinkles cut by impressed spiral lines, forming a rather coarse, 
unevenly developed texture, much as in P. mungwana and superba. 
The aperture is somewhat produced at base, and the inner lip is thick- 
ened posteriorly. Specimens apparently adult measure: 
Length, 36.5mm.; diameter, 18.0 mm.; length of aperture, 17.0 mm.; 3) whorls 
remaining. | 
Length, 27.0 mm.; diameter, 15.7 mm.; length of aperture, 14.5 mm.; 2 whorls 
remaining. | 
Length, 32.0 mm.; diameter, 15.0 mm.; length of aperture, 15.0 mm.; 3 whorls 
remaining. ah 
Length, 21.5 mm.; diameter, 15.0 mm.; length of aperture, 13.3 mm.; 2 whorls 
remaining. 
The spiral cords are not present in the earlier part of the neanic 
stage, occupying from two to three whorls only. The earlier whorls are 
nearly flat, with the minute sculpture described above (Pl. XXV, fig. 
1f; 14.5 mm. long). 
Potadoma ponthiervillensis mut. spoliata (Dupuis and Putzeys) 
Plate XXV, Figures 2—2f 
Melania ponthiervillensis var. spoliata Dupuis and PutzEys, 1900, Ann. Soc. 
Malacol. Belgique, XX XV, Bull. Séances, p. xv, fig. 24. | 
Lualaba River at Wanie-Rokula.and Ponthierville (Dupuis Coll.; type locality 
not designated). | 
Stanleyville, in a brook near the Falls of the Congo River; also 
Stanleyville without more definite location; about 320 specimens (H. 
Lang Coll.) 
This strain differs from ponthiervillensis by having only weak traces 
of spiral cords, and by the uniformly elongate shape; there are no short, 
broad individuals, and none:attaining the size of the largest ponthier- 
villensis. In the minute sculpture and the color they are like ponthier- 
villensis. Specimens measure:, 
Length, 29.0 mm.; diameter, 13.5 mm.; aperture, 14.0 mm.; — 246 whorls 
remaining. 
Length, 28.5 mm.; diameter, 13.0 mm.; aperture, 12.5 mm.; 3% whorls 
remaining. 
Length, 26.0 mm.; diameter, 15.0 mm.; aperture, 15.0 mm.; 2% whorls 
remaining. 
Intergrading individuals connecting spolata with ponthiervillensis 
are extremely rare and none seen is fully intermediate. Pl. XXV, figs. 
2, 2a, 2b represent specimens which partially bridge the gap. The upper 
and peripheral cords are moderately strong, the former characteristically 
knotted. This form is what Dupuis and Putzeys figured for spolzata, 
