178 Bulletin American Museum of Natural History [Vol. LITI 
The operculum (Plate XIX, figs. 8 and 9) is moderately concave 
externally, its cuticle finely laminate. The columellar margin is somewhat 
concave in its apical half. The apex is rectangular, pointed. Inside it 
has a more or less pinkish gray color in the young stages, but in the old 
it is largely buff. The scar is relatively small, occupying much less than 
half the total width; it encloses a smooth area rather large in the young, 
but which narrows more or less with age; around it there is quite irregu- 
larly developed rugosity concentric to the nucleus. Length, 39 mm. ; 
width, 26.5 mm. 
This species appears to be related to Pila wernei. It differs by the 
far wider umbilicus and the conspicuously shorter adnate portion of the 
innerlip. Itneeds comparison with P. kordofana, which we have not seen. 
Young shells, 25 or 30 mm. long, show a minute spiral sculpture like 
that of P. microglypta, but not so well developed. This gradually dis- 
appears with age and becomes faint or only visible in places in adult 
shells. The narrower scar of the operculum readily separates such young 
adults from microglypta. 
In some of the examples of the type lot a horizontal ledge below the 
suture scarcely exists, the whorl sloping there as in Pl. XV, fig. 3, yet 
there seem to be transitional examples. The same two forms occur at; 
Niangara, in the Uele drainage. The Stanleyville specimens appear to be 
usually free from malleation, but sometimes show small traces. Part 
of those from Niangara are similar, but others are profusely malleate in 
an intermediate stage of growth, generally smooth before and after this 
stage. 
Some account of the soft parts is given under the generic head 
(Fig. 14). 
“These large snails (Pzla congoensis) do not occur in places subject 
to desiccation by seasonal droughts, nor in rivers with strong current, 
their principal habitats being muddy, practically stagnant swamps 
largely overgrown with aquatic plants and connected with the larger 
streams. Most of these mollusks stay but a few inches and seldom more 
than a foot below water level, and are often imbedded in the softer 
surface mud. 
_ “At certain seasons the natives collect them in great quantities for 
food purposes. But among all the tribes of the northeastern Congo only 
the older people partake of this dish, the younger ones being afraid of 
even using the utensil they have been boiled in. The snails are cooked 
in water with wood ashes, taken from the shell, cleaned, cut to pieces, 
stewed again, seasoned, and served with palm oil. 
