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THE VOYAGE OF H.M.S. CHALLENGER. 
margins nearly parallel. Front deflexecl and rather narrow, with the anterior margin 
slightly arcuated and entire, or with an obscure median notch. Epistoma transverse. 
The ridges of the endostome are obsolete or imperfectly defined. The post-abdomen of 
the male is distinctly seven-jointed and it does not occupy nearly the whole width of the 
sternum at the base. The orbits are rather large, normally excavated, their superior margins 
are not (as in Scalopidia) nearly continuous with the front and antero-lateral margins; 
the eyes have the cornese normally developed, the margins acute, ciliated. The antennules 
are transversely plicated. The basal joint of the antennae is rectangular and usually does 
not reach the front ; the flagellum is somewhat elongated. The exterior maxillipedes, 
when closed, have no interspace between them ; the iscliium-joint is longitudinally 
sulcated and is not produced at its antero-internal angle ; the merus is truncated, shorter 
than the ischium, and is considerably produced at its antero-external angle ; the following 
joint is articulated at the antero-internal angle of the merus, which angle is usually 
slightly emarginated. The chelipedes are subequal and of moderate size; merus trigonous 
and short ; carpus with a spine on its interior margin ; palm short and compressed, fingers 
distally acute. The ambulatory legs are moderately elongated, with the joints slender 
and unarmed ; dactyli styliform. 
From Scalopidia this genus is at once distinguished by the normally excavated 
orbits, and from Typhlocarcinus by the larger orbits, the form of the eye-peduncles and 
of the merus of the- exterior maxillipedes, whose merus-joint is produced at the antero- 
external angle. It is much more nearly allied to Rhizopa, but, if I have rightly identified 
specimens in the British Museum collection with this genus, the form of the merus of 
the exterior maxillipedes will also, perhaps, suffice to distinguish it generically. 
The following species have been referred to Ceratoplax : — 
Ceratoplax ciliata, Stimpson. North China Sea (20 fathoms); Torres Strait. 
Ceratoplax arcuata, Miers. North Australia, Port Darwin (12 fathoms); South 
of New Guinea (28 fathoms). 
Ceratoplax (?) Isevis, Miers. Arafura Sea (32 to 36 fathoms). 
Ceratoplax ciliata, Stimpson (PL XIX. fig. 3). 
Ceratoplax ciliata, Stimpson, Proc. Acad. Nat. Sci. Philad., p. 96, 1858. 
Torres Strait, August 1874 (a female). This specimen has the dorsal surface of the 
carapace clothed with a few hairs ; the ambulatory legs, although compressed, are rather 
slender. 
Adult ?. 
Lines. Millims. 
Length, of carapace, 
. . n 
3 6-5 
Breadth of carapace, 
4 8-5 
