84 
THE VOYAGE OE H.M.S. CHALLENGER. 
Subfamily 2. Mithracdl®. 1 
Mithracinx, Miers, Journ. Linn. Soc. Lond. (Zool.), vol. xiv. p. 666, 1879. 
Carapace broadly triangulate or ovate-triangulate, sometimes transverse, with the 
sides slightly arcuate, interorbital space narrow. Rostrum short or obsolete-. Second 
joint of antennae not dilated. Chelipedes with the fingers excavated at the tips. 
In this subfamily are included those Periceridae which most nearly approach the 
Cancridee in the form of the carapace, the obsolescence of the rostral spines, the small and 
completely defined orbits, the short epistoma, and the form and development of the 
chelipedes and ambulatory legs. 
Mithrax, Leach. 
Mitlirax (Leach), Latreille, in Cuvier, Regne Animal, ed. 1, p. 23, 1817. 
„ Milne Edwards (part), Hist. Nat. Crust., vol. i. pp. 317, 320, 1834. 
,, Miers, Journ. Linn. Soc. Lond. (Zool.), vol. xiv. p. 667, 1879. 
The carapace is depressed or moderately convex, sometimes longer than broad, but 
usually transverse and very broadly rounded at the branchial regions ; dorsal surface 
uneven, tuberculated or spinose. The spines of the rostrum are usually very short, 
tuberculiform or even obsolete, but rarely well developed and acute. The orbits are 
small, well defined, armed with tubercles or short spines, or, rarely, entire. The 
epistoma is transverse, the post-abdomen in the male is distinctly seven-jointed. The 
eyes are small. The basal antennal joint is armed with a spine or tubercle at its distal 
extremity, followed usually by one or two on the exterior margin, and is very much 
enlarged ; the following joints are not dilated, and the flagellum is short. The merus- 
joint of the exterior maxillipedes is usually truncated at the distal extremity, and 
emarginate at the antero-internal angle, and with the antero-external angle sometimes 
somewhat produced. The chelipedes, in the adult male, are well developed, and some- 
times large and massive, with the palm dilated and compressed, fingers, when closed, 
with a wide intermarginal hiatus; more rarely they are more slender, with the fingers 
nearly meeting when closed. The ambulatory legs are of moderate length, sometimes 
spinose ; dactyli nearly straight or slightly curved. 
The species are rather numerous, and are, I believe, confined to the coasts of America 
and islands adjacent ; they sometimes inhabit considerable depths. 
They have already been enumerated and described by A. Milne Edwards in his fine 
work above cited. In the list which follows a few are added which have since been 
described, and a somewhat different arrangement is adopted. The genus Nemausa, 
A. Milne Edwards, is here regarded as a subgenus of Mithrax. 
1 The subfamily Othoniinse, including the two genera Othonia, Bell, and Gyclocmloma, Miers, is not represented in 
the Challenger collection. 
