136 
THE VOYAGE OF H.M.S. CHALLENGER. 
The basal antennal joint in this species is united in the adult somewhat broadly with 
the inferodateral process of the front at its antero-internal angle, but it does not enter 
the interior orbital hiatus. 
Leptodius, A. Milne Edwards. 
Leptodius, A. Milne Edwards, Ann. d. Sci. Nat., ser. 4, vol. xx. p. 283, 1863; Nouv. Archiv. 
Mus, Hist. Nat., vol. ix. p. 221, 1873. 
Chlorodius (sect. 2), Dana, U.S. Explor. Exped., vol. xiii., Crust. 1, p. 207, 1852. 
Xanthodius (subgenus), Stimpson, Ann. Lyc. Nat. Hist. New York, vol. vii. p. 52, 1859. 
In this genus the carapace is widely transverse, somewhat depressed, and very 
distinctly lobulated in its anterior half, posteriorly nearly plain ; the frontal margin is 
truncated and slightly sinuated, with a median notch or fissure ; the antero-lateral 
margins are longer than the postero-lateral margins, and are normally divided into four 
teeth or lobes, besides the exterior orbital tooth, which is usually obsolete ; behind the 
last anterodateral tooth are occasionally one or two smaller teeth on the postero-lateral 
margin ; the marginal teeth are usually dentiform, not rounded as in Actseodes. The 
post-abdomen in the male is five-jointed; the three intermediate segments coalescent and 
forming a single joint. The superior margins of the orbits are marked with two slight 
notches and fissures. The basal antennal joint reaches the infero-lateral process of the 
front or even enters slightly within the interior orbital hiatus. The merus of the 
exterior maxillipecles is truncated or slightly notched at the distal extremity, and its 
antero-internal angle is slightly emarginate or sinuated; its antero- external angle is often 
slightly produced. 
The chelipedes in the adult male are moderately developed ; the merus or arm is short 
and almost invariably covered in a dorsal view by the antero-lateral margins, carpus 
dentated on the inner margin, palm not cristated above, fingers excavated at the distal 
extremity. The ambulatory legs are moderately developed, with the fourth to the sixth 
joints slightly compressed, but not carinated or spinose ; dactyli styliform. 
This genus may be considered the representative in the Chlorodiinse of Xantho in the 
Cancrinse ; it is also nearly allied to Carpilodes, Actseodes, and to the genus which follows 
( Phymodius ). 
From Carpilodes and Actseodes it is usually to be distinguished by the dentiform or 
tuberculiform antero-lateral marginal teeth, not to speak of other characters. 
The species are somewhat numerous ; several inhabit the Indo-Pacific region. Two 
species, Leptodius macandrese and Leptodius punctatus, occur in the West Atlantic or at 
the Canaries and Cape Verde Islands. The others inhabit the American coasts from 
Florida to Brazil, and from California to Chili. One species (Leptodius cooksoni ) occurs 
at the Galapagos. None, I believe, have been recorded from very deep water. They 
may be distributed under two subgeneric divisions or sections as follows : — 
