164. Bulletin American Museum of Natural History [Vol. LIIT 
Length, 28.0 mm.; width, 23.5 mm.; convexity, 11.5 mm. 
oe 24.3 Ue pp a ELS 
In brackish water, at Malela, the size is much reduced, and the 
features of youth persist. The auriculate stage appears to be well 
developed in few individuals. 
Length, 14.0 mm.; width, 13.3 mm.; convexity, 6:7 mm. 
a 14.0 pants nS) i Fe 
a 13.5 kes 0 % 6.5 
‘When we stepped ashore at Zambi Dr. Bequaert at once pulled a 
' few of these beautiful large Neritina (Neripteron) cweniana from the 
limestones just below the surface of the water. Our host, Dr. René van 
Saceghem, called our attention to others that had fastened themselves 
to a nearby cement wall. Later on, when criss-crossing the Congo in the 
neighborhood, I found a much greater number on submerged, dead, 
anchored or floating branches or sticks generally no more than two feet 
below the surface. They showed themselves very susceptible to disturb- 
ances and instantly let go their hold when a branch or any other object 
upon which they were sitting was lifted quickly out of the water. When 
the receding tide might leave them stranded they let themselves drop 
before they were even completely uncovered. Though mo:t of them 
sank like stones they can swim with ease. Perhaps their strongly flat- 
tened shell and large, expanded, winged lip help offer additional support 
to the mantle. In avoiding exposure they certainly behave differently 
from their two smaller relatives NV. glabrata and adansoniana, found near 
or at the mouth of the Congo, which do not seem to be affected by being 
left dry during low tide. N. oweniana were common about and below 
Zambi but scarce farther up-river. Undoubtedly the salinity of the water 
is enough different there to be an important factor, since two crabs, 
Sesarma (Holometopus) biittikoferi and angolense, also begin to be com- 
mon about Zambi and farther downstream. Some of the largest speci- 
mens of oweniana were taken in the neighborhood of Zambi (about 27 
miles from the mouth), always in places with a fairly strong current. 
They were scarcer at Malela (about 12 miles from the mouth) and prac- 
tically absent from Banana where I looked especially for them. Only 
once, a few miles up Banana creek, did I find two on a floating branch.” 
CEE i.) 
} _ THEopoxus Denys de Montfort 
Theodoxus DENYS DE MontrFort, 1810, ‘Conchy]l. Systém.,’ IT, p. 351 (Theodoxis 
on p. 350, under the figure). Monotype: Theodoxus lutetianus Denys de Montfort = 
Nerita fluviatilis Linnzeus. 
