1927], _——- Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo: = § 2% 
The shell is solid, either smoothish, spirally lirate, or carinate, never having axial 
ribs or folds; color uniform or but little variegated, brown, olivaceous, or yellowish. 
Aperture ovate, the basal lip more or less produced; outer lip straight or nearly so 
in profile; the callus of the inner lip thickened near the posterior angle. Operculum 
ovate, of about three whorls, of which the first two form a small spiral figure, and the 
last widens rapidly; the nucleus situated between the lower third and fourth, near the 
columellar side; scar of attachment narrow, less than half the total width (Fig. 450, 
P. liricincta walikalensis). 
Edge of the mantle smooth and even. Animal apparently oviparous; externally 
uniform black in species examined. The radula is-relatively large and very long 
(8.5 mm. long and 0.5 mm. wide in a specimen of P. p. spoliata of 11 mm. diameter). 
The squarish central tooth has few denticles, 3 on each side of the very prominent 
central one; the body below it is mesially swollen, showing the usual Troschel lines, 
the platform line! continuous downward from the embayment line.2 The lateral 
tooth has a distinct embayment line and supporting plate.? The marginal teeth have 
three denticles each (Fig. 45a, Potadoma ponthiervillensis spoliata). 
Distribution: West and Central Africa, in streams draining into 
the Atlantic and Lake Albert (Map 8). 3 
The early neanic whorls never show coarse spiral sculpture. When 
this is present, it arises in a mid-neanic stage and is generally most fully 
expressed in the adult stage. The only exception we have noticed is 
seen in P. schoutedeni, in which the acme of sculpture falls in a late 
neanic stage, and is nearly or wholly obliterated in the last whorl. The 
relatively late appearance of coarse spirals in ontogeny apparently denotes. 
rather recent evolution of this character in the genus. This contrasts 
with Melanoides, in which such sculpture appears at the beginning of the 
neanic stage in all species of which young stages were examined. 
Potadoma is related to the Indo-Chinese genus Brotia* and the 
Javan Sulcospira. Both of these differ from the African genus by the 
absence of callus on the parietal wall of the shell, by the nearly circular 
‘“paleomelanid”’ operculum with larger spiral figure and more slowly 
widening last whorl, and by the viviparous reproduction. 
ea ome 
1‘*Rampenlinie”’ in the Troschelian terminology. 
ee ee 
3 Stitzplatte.” 
4Brotia EL. Apams, 1866, Proc. Zool. Soc. London, p. 150. Monotype: Melania pagodula Gould. 
Melania subgenus Acrostoma Brot, 1870, American Journ. Conchol., VI, 2, Appendix, p. 272, for 
two species, among them M. hiigelii Philippi, but type not designated; 1874, in Martini and Chemnitz, 
‘Syst. Conch. Cab., I, 24, Melaniaceen,’ p. 6, with M. hiigelii Philippi, of India, designated astype. Not 
_Acrostoma Le Sauvage, 1826. : : : 
aM elania section Dioieia ROVERETO, ier Atti Soc. Ligustica Sc. Nat., X, p. 109. Substitute for 
Brot, 1870. Not Brotella Kaup, 8. sp as 
Ae CossMANN, 1900, Rev. de Paléozool., IV, p. 42. Substitute for Brotella Rovereto, 
189 
” esaaaeae (1920, Rec. Indian Mus., XIX, p. 109; 1921, op. cvt., XXII, p. 559) is the chief authority 
on the characters of this genus. It comprises large melanians of the regions from southern China to 
India. ; 
of this group appears to be as variable as the shells, and we are not yet wholly satisfied 
ane Bulehnas Tropebel ( 1857, ‘Das Gebiss der Schnecken,’ p. 114; monotype: Melania sulcospira 
 Mousson), has similar operculum and dentition, and is also viviparous. The shell is somewhat different, 
and the mantle margin and terminal genital ducts need comparison. Yet it seems likely that no differ- 
ential characters of importance exist between Sulcospira and Brotia (Acrostoma). 
