112 
William F. Adams 
during February 1986 indicate a range of 0 parts per thousand (ppt) to 5 
ppt when the lake was being reimpounded after a drawdown and there 
was no water being released from the lake. Concentrations up to 3 ppt 
were observed during normal summer releases from the lake. Hopkins 
et al. (1973) note that R. cuneata is restricted to areas where salinity is 
below 15 ppt most of the time and may occupy portions of creeks and 
tidal rivers where salinities are continuously below 1 ppt for extended 
periods. 
DISCUSSION 
Distributions of many species in the lake appear to be spotty based 
on the collection station records (Table 2). Differences between stations 
may be caused by microhabitat conditions, by disturbance histories, or 
by differing efficiency of collecting at each station. Species of mollusks 
not recorded in this survey may yet be found to exist in the lake. 
Misidentifications in Historical Records 
The record of Laevape x diaphanus by Dawley (1965) may be based 
on a misidentification of L. fuscus\ she did not mention the source of 
the specimen or the determination. Laevape x diaphanus typically inhabits 
rock bottoms in slowly flowing waters, and I have collected it on debris 
in swamp streams near Wilmington. However, L. fuscus is fairly common 
in southeastern North Carolina, and it would be more likely than L. 
diaphanus to have occurred in the lacustrine habitats provided by the 
lake. 
Campeloma geniculum may also have been misidentified, because it 
is difficult to separate from C. decisum. In discussing current taxonomy 
of the genus Campeloma , Clench (1962) correctly remarked that “few 
genera among our North American freshwater mollusks are in a more 
confused state.” Bailey (1940) states that Pilsbry examined specimens of 
C. geniculum from the lake and referred to them as “a rather unusually 
rounded form of the species.” That would imply that the specimens may 
have been C. decisum, which is separated from C. geniculum by its 
more rounded shoulders (Burch 1982). Rehder (1949) collected C. 
rufum (which would now be synonymized with either C. geniculum or 
C. limum , see Synonymy above) from Lake Waccamaw, approximately 
50 km W of the study area, as well as from Greenfield Lake. Campeloma 
that had characteristics of both C. geniculum and C. decisum were 
noted by Porter (1985) in his collections from Lake Waccamaw, and 
one specimen that had characteristics of C. geniculum was found during 
the present survey. Campeloma geniculum is generally expected to have 
a more southern range, but a population is certainly possible in south- 
eastern North Carolina. 
