5 



prominent, differently shaped. Carapace subcircular, longer 



than broad 6 



Walking legs short, scarcely longer than breadth of cara- 

 pace; dactyli straight, conical, gradually tapering to tip. 

 Rostrum triangular, nearly vertically deflexed and fixed. 

 Carapace transversely oval, broader than long; sides un- 

 armed. Sides of carapace and legs covered by thick, club- 

 shaped hairs, particularly long at sloping sides of the 

 former, and on meropodites of legs. Very small species, 



breadth of carapace 5 — 6 mm Elamenopsis A. Milne-Edwards 



6. Rostrum trilobate, triangular or truncate Hymenicus Dana 



Rostrum trispinose Rhynchoplax Stimpson 



Hymenosoma Desmarest. 

 1825. Hymenosoma Desmarest. Cons. s. 1. Crust, p. 163. 



Though this genus has been known since nearly a century, its true characters remained 

 rather insufficiently indicated. H. Milne-Edwards ^) first pointed out the absence of an epistome, 

 but this important feature appears to have been overlooked by Haswell *), who advocated the 

 view, that all the genera (at least Hymenosoma^ Hymenicus and Halicarcimis) should be united 

 into the original genus that gave its name to the whole group, which he called, however, 

 Hymenicitiae, following Dana. Haswell's opinion has been shared by Australian carcinologists, 

 such as Baker *), Fulton and Grant *). Stebbing, however, recently '') argues, that Hymenosoma 

 is distinguished, at least from Halicarcinus, by the much narrower shape of the merus and 

 ischium of the external maxillipeds, and by the long hairs fringing the propodite and dactylus 

 of the walking legs, which joints are spineless. 



The absence of an epistome, the characters of the walking legs, and the narrow abdomen 

 of the cf , that reaches only to the middle of the nearly circular sternum, are all characters, that 

 sharply separate at least the typical species of Hymenosoma from Hymenicus and Halicarcinus. 



Though a rather large number of species has been assigned to Hymenosoma^ only two 

 species appear to have their proper place here ; they may be distinguished thus : 



Flattened part of carapace longer than broad (not including the 

 rostrum); external orbital angle sharp, bifid and spine-like; 

 walking legs rather short, about twice the breadth of the 

 carapace. Abdomen of cf narrow, reaching up to the middle 

 of the sternum. Species of South Africa H. orbiculare Desmarest 



1) Hist. nat. Crust., t. 2, 1837, p. 35 — 36. Ann. Sc. Nat. (3) t. 20, 1853, p. 222. 



2) Cat. Austral. Crust., 1882, p. 114. 



3) Transact. R. Soc. South Austr., Adelaide, v. 30, 1906, p. 114. 



4) Pvoc. R. Soc. Victoria, v. 15, 1902, p. 59. 



5) Transact. R. Soc. Edinburgh, v. 50, prt 2, 1914, p. 270. 



5 



