102 A HISTORY OF RECENT GKUSTACEA 



attention for the sake of the species Halicarcinus planatus 

 (Fabricius), whicli 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 Elwmene Mathcei of Milne- 

 Edwards is probably the young male of this species, and 

 that it is quite distinct from the original Ilymenosoma 

 Mathcei of Desmarest. 



8copimera, de Haan, 1833, was established for the 

 single species, Scopimera globosa, 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. This 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.' 



BotiLla, Stimpson, was substituted for Boto^ de Haan, 

 1833, a pre-occupied name. In this genus BotiLla fenes- 

 trata, Hilgendorf, from the East Coast of Africa, has the 

 windows or tympana also in the sternum. Botilla brevi- 

 tarsis, de Man, is from the Mergui archipelago. Dr. de 

 Man makes Sccypimera a synonym of Botilla, but, if the 

 two genera are united, Scopimera as the older name must 

 take precedence. 



Hexapus, 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, MievB, 1881, 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 



