102 A HISTORY OF RECENT CRUSTACEA 
attention for the sake of the species Halicarcinus planatus 
(Fabricius), which is widely distributed over the Antarctic 
or Austral region, being the only Brachyurous Decapod, 
it is said, proper to that wide area of distribution. Mr. 
Haswell considers that the Elamene Mathai of Milne- 
Edwards is probably the young male of this species, and 
that it is quite distinct from the original Hymenosoma 
Mather of Desmarest. 
Scopiméra, de Haan, 1853, was established for the 
single species, Scopimera glebosa, in which the arm of 
the chelipeds and the corresponding fourth joint (the so- 
called merus) of the hinder legs has the outer margin 
cartilaginous instead of crustaceous, with a transparent 
membrane in the flat part. his. peculiarity explains 
de Haan’s choice of a generic name, which means ‘ thighs 
with windows in them.’ From the resemblance to the 
head of a drum these membranous pieces have been called 
‘tympana.’ 
Dotilla, Stimpson, was substituted for Doto, de Haan, 
1833, a pre-occupied name. In this genus Dotilla fenes- 
trata, Hilgendorf, from the East Coast of Africa, has the 
windows or tympana also in the sternum. Dotilla brevi- — 
tarsis, de Man, is from the Mergui archipelago. Dr. de 
Man makes Scopimera a synonym of Dotilla, but, if the 
two genera are united, Scopimera as the older name must 
take precedence. 
Hexipus, de Haan, 1835, is entirely devoid of the 
last pair of walking legs, so that instead of decapods these 
crabs have become octopods, and if the chelipeds are 
excluded and only the walking legs counted they may be 
regarded as hexapods, or six-legged crabs, and to this 
view the name of the genus refers. 
Thaumastoplax, Miers, 1381, it is said, ‘is closely allied 
in all its characters and particularly in wanting the fifth 
pair of thoracic legs, to the genera Hexapus, de Haan, 
and Amorphopus, Bell, but is distinguished from the former 
by the much greater development of the second ambula- 
tory legs and the structure of the outer [third] maxilli- 
pedes, whose merus [fourth] joint is elongated and 
