2 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 120 
As the group becomes better known, identifications become easier 
only in certain directions. In the present work some clarification is 
effected by recognizing the validity of species previously synonymized. 
As more species are discovered, however, the distinctions between 
them become narrower, and the difficulties of relating them to the 
older descriptions increase. Until type material is reexamined and 
redescribed, several groups must remain confused. In the present 
work these are termed “‘complexes,” and the Portunus gladiator and 
P. longispinosus complexes have caused particular difficulty. 
A more fundamental problem concerns the importance attached to 
differences in male secondary sexual characteristics. Shapes of male 
abdomens have long been recognized as having diagnostic importance, 
and since Stephenson (1945), following Brocchi (1875), increasing 
stress has been laid upon male first pleopods. 
In both these structures the extent of ‘‘expectable” variation has 
been known in general terms, and few cases of greater variation have 
been described (e.g., male pleopods of P. orbitosinus by Gordon, 19388, 
and male abdomens of P. granulatus by Crosnier, 1962). In the pres- 
ent work unexpected variability in male pleopod structure has been 
noted in several cases. In one species (P. orbitosinus) there is approxi- 
mately continuous gradation between wide extremes, and in three 
others (Thalamita stimpsoni, T. danae, and Portunus argentatus) there 
is distinct male dimorphism. If a species is defined in terms of a dis- 
tinct morphological gap between two forms, 7’. stimpsoni, T. danae, 
and P. argentatus should each be split into two species. However, 
apart from male pleopods and abdomens, no structural differences 
could be found. For the purposes of the present paper, P. argentatus 
was taken as a “‘test case” of the concept of a portunid species (see 
p. 19). This concept implies a distinct morphological gap in general 
facies, as well as in the shape of the male abdomens and structure of the 
male pleopods. If no distinctions were noted in general facies, groups 
with different pleopods are here recorded as different “forms.” Pos- 
sibly they are incipient species. 
Details of synonymy vary from species to species; where there had 
been past confusion, reasonable detail is given, but in other cases only 
critical references are cited. Brief morphological comments are given 
upon species adequately treated in recent literature, and fuller rede- 
scriptions are restricted to inadequately described species. Subfamily 
headings follow Stephenson and Campbell (1960) ; within subfamilies 
genera are in alphabetical order, and within genera species are also in 
alphabetical order, except where similar species are grouped into 
‘“complexes.”’ 
