56 
THE VOYAGE OF H.M.S. CHALLENGER. 
straight, slender, simple and divergent from the base. Post-abdomen (in the male) 
distinctly seven-jointed. Eyes completely retractile within the small orbits, which have 
a lateral aspect and a fissure or hiatus in the upper and lower margins. Basal antennal 
joint moderately enlarged, with or without a spine at the antero-external angle, the 
flagellum usually exposed and visible at the sides of the rostrum in a dorsal view, but 
sometimes partially concealed. Exterior maxillipedes with the merus-joints distally 
truncated ; the antero-external angle slightly produced and rounded, the antero-internal 
angle emarginate. Chelipedes in the adult male with the palms either slender or 
moderately enlarged ; fingers, when closed, with or without a slight intermarginal hiatus. 
Ambulatory legs moderately elongated (the anterior pair usually much the longest), with 
the joints subcylindrical and unarmed ; the dactyli nearly straight. 
The species, most of which have been enumerated by A. Milne Edwards, 1 are rather 
numerous, and occur commonly in the shallower waters of the Indo-Pacific region, to 
which this genus is apparently restricted. They may be conveniently arranged under 
the following sections, which are connected by insensible gradations. 
1. Carapace smooth and even above, with none or with a few long spines. Basal 
antennal j oint usually without a spine at its antero-external angle. Cheli- 
pedes (in the male) with the palms small and slender. Hyastenus diacanthus, 
(de Haan) ; Hyastenus aries (Latreille) ; Hyastenus spinosus (A. Milne 
Edwards) ( Hyastenus verreauxii, A. Milne Edwards, is probably a variety 
of Hyastenus diacanthus). 
2. Carapace with the dorsal surface uneven and tuberculated, but without long 
spines. Basal antennal joint usually with a spine or tubercle at its antero- 
external angle. Chelipedes in the male with the palms sometimes enlarged. 
(. Hyastenus , White ; Chorilia, Dana ; Lahaina, Dana ; Lepidonaxia, Targioni 
Tozzetti). 
(The name Hyastenus, which was used for the first section in my revision of the 
group in 1879, cannot be retained in that sense, since in the type, Hyastenus sebx, 
White, the carapace is somewhat tuberculated.) 
Species : — Hyastenus sebse, White ; Hyastenus planasius, Adams and White ; 
Hyastenus pleione (Herbst) ; Hyastenus oryx, A. Milne Edwards ; Hyastenus longipes 
(Dana); Hyastenus gracilirostris, Miers; Hyastenus japonicus, Miers; Hyastenus ovatus 
( Dana) ; Hyastenus sinope ; Hyastenus elegans, described below ; Hyastenus convexus, 
Miers; (this species and Hyastenus planasius have a nearly smooth carapace, as the 
species of the first section). Pisa fascicularis, Krauss, from Natal, may be referable 
here, but the orbits are shown in the figure as entire above. 
1 Nouv. Archiv. Mus. Hist. Nat., vol. viii. p. 249, 1872. 
