No. 3567 LABIDOCERA JOLLAE GROUP—FLEMINGER 45 
cool period. This in effect would trap one segment in the upper 
Gulf of California while the Pacific coast population retreated north 
of Magdalena Bay. Parallels have been noted in the temperate 
fishes of the two regions and accounted for by the same reasoning 
(Hubbs, 1948; Walker, 1960). Following isolation of the daughter 
populations, it is likely that the initial adaptations were physiological 
since the chemical, physical, and climatic properties of the two regions 
show notable differences. The distinguishing morphological features, 
centered in sexual structures, could have come about by reinforcement, 
in response to subsequent genetic exchange between the two popu- 
lations during especially cold periods. 
In the above discussion the action of reinforcement has been pro- 
posed as the basis for explaining the extant patterns of morphology 
with respect to range. Examination of other closely related com- 
plexes should be made to obtain more direct evidence that reinforce- 
ment occurs in planktonic populations; that is, we should determine 
whether species-specific differences in an area of overlap between 
closely related species would be more pronounced than in the allo- 
patric portions of the range of each. Study of Fleminger’s (1964) 
trispinosa group (genus Labidocera) has yielded evidence of reinforce- 
ment in several morphological features and will be presented elsewhere 
in the near future. 
Assuming that reinforcement of reproductive isolation is the basis 
for the extant morphological patterns in the jollae group, why is it 
that no pair of species has successfully adapted to some degree of 
sympatry? In the trispinosa group, each pair of adjacent species 
share several hundred miles of common range but each species’ range 
also includes a more extensive nonoverlapping segment. Another 
point to consider is whether reinforcement is evidence that the tri- 
spinosa group is in an earlier stage of development than that attained 
by the jollae group. Further study of the biology and distribution of 
these groups should prove enlightening as to the mechanics of disper- 
sion, gene flow, and competition among planktonic Crustacea. 
Summary 
Three closely related species inhabiting coastal waters of western 
North America and referable to the genus Labidocera are described. 
Two of the species are new. Geographical relationships among the 
three species are established and morphological differences compared 
between allopatric and incompletely sympatric pairs. The location 
and strength of character differences in the light of geographical re- 
lationships is noted and the likelihood that reinforcement of secondary 
sexual characters has played a major role in evolution within the group 
is discussed. Mating behavior within the group is also considered. 
