224 
THE VOYAGE OE H.M.S. CHALLENGER. 
have examined). The post-abdomen in the male is distinctly seven-jointed, and covers 
the whole width of the sternum at the base between the bases of the fifth ambulatory 
legs. The eye-peduncles are short and robust. The antennules are transversely plicated. 
The basal antennal joint is slender, and occupies the interior hiatus of the orbit, and its 
distal extremity is free, not united to the front. The merus of the exterior maxillipedes 
is shorter than the ischium, truncated or slightly rounded at the distal extremity, and 
the next joint is articulated at its antero-internal angle. The chelipedes (in the male) 
are subequal and moderately robust ; merus trigonous ; carpus with a spine or tooth on 
its interior surface ; palm short, rounded above and below ; fingers clistally acute and 
denticulated on the inner margins. The ambulatory legs are somewhat elongated, with 
the joints subcylinclrical ; dactyli slender, styliform, but slightly compressed and not 
ciliated. 
The genus Geryon is very nearly allied both to Pseudorhombila and Pilumnoplax, 
and to the Cancroid genus Galene ; it is distinguished from them by the considerable 
development of the lateral marginal spines of the carapace, and from Pseudorhombila, as 
figured by Milne Edwards, by the more slender basal antennal joint, which does not 
reach the front. 
The species, which occur at considerable depths in the North Atlantic, may attain a 
large size. The following have been described : — 
Geryon tridens, Kroyer. Danish and Scandinavian Coasts; off Valentia, Ireland 
(80 to 808 fathoms). 
Geryon quinquedens, Smith. Nova Scotia and East Coast of the United States 
(to 740 fathoms). 
Geryon longipes, A. Milne Edwards. Mediterranean and North Spanish Coasts 
(to 700 metres). 
Geryon (?) incertus, n. sp. Off the Bermudas (435 fathoms, Station 33). 1 
Geryon (?) incertus, n. sp. (PI. XVI. fig. 3). 
This species is represented in the collection by the carapace of a single specimen 
(probably immature), since it is of very small size, and as the fifth ambulatory legs are 
deficient, I am somewhat uncertain as to its generic identification. It may belong to a 
genus of the Portunidee, near to Bathynectes, where I originally placed it. 
The carapace is little broader than long; its surface is very uneven and marked 
with transverse granulated ridges, of which there are two on the gastric region, placed 
one on either side of the median line, and one (a continuous ridge) crossing the 
1 On account of the form of the basal antennal joint, which is said to resemble that of Galene, de Haan, the genus 
Clialsepus, Gerstsecker, is identified with Geryon, rather than with Pseudorhombila, but the identification is somewhat 
uncertain ; the typical species Ghaleepus trispinosus (Herbst), is said to occur in the East Indies. 
