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THE VOYAGE OF H.M.S. CHALLENGER. 
joints compressed and longitudinally sulcated ; in the fifth legs these joints are usually 
smooth, and as in other Portunidse, considerably dilated ; the terminal joint is oval and 
lamelliform. 1 
The species of the genus Neptunus thus defined are very numerous, and occur in all 
the warmer temperate and tropical seas of the globe. Neptunus sayi is a pelagic and 
widely-distributed species, occurring commonly on the floating gulf-weed. Most of the 
species are, I believe, sub-littoral or shallow-water forms ; several, however, have been 
recorded from depths varying between 20 and 50 fathoms, and the remarkable Neptunus 
( Hellenics ) spinicarpus occurs usually at much greater depths, and has been taken by the 
Challenger off the coast of Brazil in (probably) 350 fathoms. 
A. Neptuni with the spine on the interior margin of the carpus of the chelipedes 
normally developed : — 
a. Carapace broadly transverse ; antero-lateral margins forming with the frontal 
margin a regular curve with long radius. Lateral epibranchial spine much 
longer than the preceding tooth. 
Subgenus, Neptunus. 
Neptunes argues, A. Milne Edwards (pt.), Archiv. Mus. Hist. Nat., vol. x. p. 316, 1861. 2 
The following are species belonging to this subgenus, which are not referred to by 
A. Milne Edwards, or have been described since the publication of his monograph in 
1861 
Neptunus mexicanus (Gerstsecker, as Euctenota) = Arenseus bidens, T. J. Smith. 
Mexico ; Nicaragua. 
Neptunus (?) pudica (Gerstsecker). Coast of Brazil. (Perhaps a species of the 
subgenus Amphitrite.) 
Neptunus trituberculatus, Miers. China and Japan. 3 
1 In the species of this genus, the merus of the exterior maxillipedes is of very variable form ; it may he (as in the 
typical species of Neptunus, Neptunus pelagicus) obliquely truncated at the distal extremity, with the antero-external 
angle rounded and not at all produced, the antero-internal angle slightly produced and rounded, or, as in the subgenus 
Achelous, de Haan (type Aclielous spinimanus), more elongated, truncated and produced at neither angle, or, as in the 
species of the suhgenus Amphitrite, de Haan (type Amphitrite gladiator), the antero-external angle of the merus may he 
considerably produced and acute. Sometimes, as in Pontus, de Haan (type Pontus convexus = Neptunus sieboldi, A. Milne 
Edwards), the antero-external angle is a right angle and the merus-joint is quadrate, sometimes, as in Euctenota, 
Gerstsecker (type Euctenota mexicana), it is produced and somewhat rounded at the distal extremity. 
2 From this section is excluded the genus Callinectes, distinguished by the _L-kkaped post-abdomen of the male 
which is regarded as distinct by A. Milne Edwards in his later work, Crust, in Miss. Sci. an Mexique. 
3 Neptunus madagascariensis, Hoffmann, is very probably a species of Callinectes. 
