210 
THE VOYAGE OF H.M.S. CHALLENGER. 
by Dana, they constitute a somewhat heterogeneous and not very well-defined group, 
generally distinguished by the extension of the exterior maxillipedes over the anterior 
margin of the buccal cavity, and the elongated flagella of the exterior antennae, and 
include forms related to widely separated families, as, for instance, Trichocarcinus, Miers 
= ( Trichocera , de Haan), which is scarcely distinguishable from the genus Cancer. 
The Challenger collection includes but two genera of this group ; the first, Hypopel- 
tarium ( = Pelt avion, Auctorum), on account of its orbiculate carapace, may be regarded 
as establishing the transition from the Corystoidea to the Cyclinea, the other, Gomeza, 
in the elongated carapace and the greatly developed flagella of the antennse, is altogether 
a typical representative of the Corystoidea. 
Hypopeltarium, n. gen. 
Peltarion, Jacquinot and Lucas, Crust, in Voy. au Pole Sud. Zool., vol. iii. p. 80, 1853 ; name 
preoccupied. 
Carapace nearly orbiculate, about as broad as long, moderately convex, with the 
dorsal surface uneven ; the lateral margins and the margins of the orbits armed with 
spinules. The front is narrow, about one-sixth the greatest width of the carapace, and 
three-spined, the median spine sometimes notched at the distal extremity. There are 
two slight incisions in the superior margins of the orbits, and a much deeper and wider 
hiatus in the inferior margin, near the exterior orbital angle. The epistoma is but slightly 
transverse. The anterior margin of the buccal cavity is not distinctly defined ; the ridges 
of the endostome are partially developed. The post-abdomen in the male is narrow 
and five-jointed, with the third to the fifth segments consolidated. The eye-peduncles 
are rather slender and of moderate length. The antennules are longitudinally plicated. 
The antennse occupy the interior hiatus of the orbits ; their basal j oints are short, but 
slightly enlarged, scarcely any wider than the following joint, which is longer than the 
basal joint and slightly compressed ; the antennal flagella, as in other Corystidse, are 
elongated, but not half as long as the carapace. The maxillipedes are normal ; the 
ischium is not produced at its antero-internal angle, the merus is subtruncated and 
spinuliferous at the distal extremity, and rounded at the antero-external angle ; the antero- 
internal angle is not emarginated. The chelipedes (in the adult male) are well developed, 
but not very large ; merus trigonous without spines ; carpus with a strong spine at its 
antero-internal angle ; palm compressed, short, spinuliferous above ; fingers robust, 
scarcely as long as the palm, and rather obscurely dentated on the inner margins, distally 
acute ; the dactylus spinuliferous on the superior margin. The ambulatory legs are 
moderately elongated, with the joints, except the dactyli, more or less granulated or 
spinuliferous ; dactyli styliform, slender, and much longer than the penultimate joints. 
The single species of this genus ( Hypopeltarium spinosulum ) is common in the 
