280 
THE VOYAGE OE H.M.S. CHALLENGER. 
subequal and ratlier slender, with the merus (in the species I have examined) short and 
rounded, or obscurely trigonous ; carpus without a spine or tooth on the inner margin ; 
palm small, compressed; fingers straight and distally acute. Ambulatory legs very 
slender and of moderate length ; dactyli nearly straight and as long as or longer than the 
penultimate joints. 
Two of the described species of this genus (which are possibly not distinct the one 
from the other) Hymenosomct orbiculare, Latreille, and Hymenosoma geometricum, 
Stimpson, occur at the Cape of Good Hope in rather shallow water; a third species, 
referred by Milne Edwards to this genus, Hymenosoma gaudichaudii, Guerin-Mdneville, 
occurs on the Australian coasts. 1 
Hymenosoma orbiculare , Desmarest. 
Hymenosoma orbiculare, Desmarest, Consid. sur les Crust., p. 163, pi. xxvi. fig. 1, 1825. 
„ „ Milne Edwards, Hist. Nat. Crust., vol. ii. p. 36, 1837 ; Crust, in 
Cuvier, Regne Anim., ed. 3, Atlas, pi. xxxv. fig. 1 ; Ann. d. Sci. 
Nat., ser. 3, Zool., vol. xx. p. 222, 1853. 
Leacluum orbiculare, MacLeay, Invert, in Smith, Zool. South Africa, p. 68, 1849. 
Hymenosoma geometricum, Stimpson, Proc. Acad. Nat. Sci. Philad., p. 108, 1858, var. (?) 
Numerous specimens were collected in Simon’s Bay, South Africa, in 5 to 20 fathoms 
(mostly of small size). 
The largest male in the series has the following dimensions : — 
Lines. 
Millims. 
Length of carapace, ..... 
51 
11-5 
Greatest breadth of carapace, rather over 
5 
11 
Length of a chelipede, .... 
6 
12-5 
Length of second ambulatory leg, rather over 
10 
21-5 
Halicarcinus, White. 
Halicarcinus, White, Ann. and Mag. Nat. Hist., ser. 1, vol. xviii. p. 178, 1846. 
„ Milne Edwards, Ann. d. Sci. Nat. ser. 3, Zool., voL xx. p. 222, 1853. 
Liriopea, Nicolet, in Gay, Hist, de Chile, Zool., vol. iii., Crust., p. 160, pi. i. fig. 1, 1849. 
This genus is very nearly allied to the preceding ( Hymenosoma ), but the typical 
species may be distinguished by the following characters : — The carapace is more transverse 
and rounded, less distinctly triangulate. The front is distinctly trilobated. The epistoma 
is transverse and distinctly developed. The basal segment of the post-abdomen in the male 
occupies the whole width of the sternum, between the bases of the fifth ambulatory legs. 
The exterior maxillipedes (in the typical species at least) are more robust, the ischium 
1 Mr. W. A. Haswell, in his recent Catalogue of the Australian Crustacea, would unite with Hymenosoma all the 
species referred by authors to Hymenicus, Dana, and Halicarcinus, White. 
