NO. 3556 PORTUNID CRABS—STEPHENSON AND REES 19 
This second form of pleopod resembles that figured by Edmondson 
(1954, fig. 14 c,d), differing only in subterminal armature which 
Edmondson shows as a distinct row of sizable bristles on the outer sur- 
face. This form of pleopod has also been figured by Crosnier (1962, 
figs. 77, 80, 81). The corresponding abdomen is apparently inter- 
mediate between those mentioned above. 
Apart from male pleopods and abdomens, no structural heterogene- 
ity could be found in the present material. There are two possibil- 
ities : 
a. The material belongs to two distinct species, separable only in 
adult males and effectively only by pleopods. To accept this would 
involve several difficulties. First, the two “species”? would be sym- 
patric in distribution, or at least seriously overlapping, since both 
occur in one collection. Second, to establish which was the true P. 
argentatus would necessarily await reexamination of Milne Edwards’ 
material. Third, it would involve the assumption of reproductive 
isolation, with females being capable of fertilization with only one or 
another type of male. Until the detailed role of pleopods in ferti- 
lization has been determined, this must remain doubtful. Fourth, 
there are other cases of heterogeneity in male pleopods (e.g., Thalamita 
stimpsom, T. danae, P. orbitosinus—see text), and these should be 
treated similarly. This presents particular difficulty in P. orbitosinus 
where pleopod variation is more continuous than in the present case. 
b. The second possibility is that a species can be polymorphic as 
regards male pleopods. 
As stated in the Introduction, for the purposes of the present paper, 
P. argentatus was taken as the ‘‘test case” of the concept of a portunid 
species. This concept implies a distinct morphological gap between 
other species in general facies as well as pleopod structure. 
Thus there are two male forms of P. argentatus, form A corre- 
sponding with that figured and described by Stephenson (1961a) and 
form B corresponding to that given in figure 2a. Possibly Edmond- 
son’s (1954) and Crosnier’s (1962) specimens belong to a third form, 
resembling form B in general shape of the pleopod, but differing in its 
much better developed bristles. 
DistripuTion.—Natal to Honolulu, including Japan and Australia. 
Portunus brockii (de Man) 
Neptunus brockii de Man, 1887a, pp. 328-331, pl. 13 (fig. 4). 
Neptunus (Hellenus) brockii de Man.—Alcock, 1899, pp. 438-44.—Shen, 1937, 
p. 111, figs. 7, 8e, 8f. 
Portunus brocki (de Man).—Stephenson and Campbell, 1959, pp. 106-107, 
figs. 2G, 3G, pls. 2 (fig. 3), 4G, 5G. 
Marerrau.—Philippines: Subig Bay, China Sea, off southern 
Luzon, shore, seine, sand, Jan. 7, 1908, Alb., 1 male; Sta. 5160, Tinakta 
