239 



whereas the palp is greatly developed, with the propodus considerably widening- distally and truncate ^). 

 Three species of this genus are now known, the type species is Atlantic. 

 Key to the species : 



1. Propodus of external maxillipeds longer than wide at its distal 



end. Third (last) pair of walking legs as long as preceding pair. 



Atlantic species Th. anomalipes Miers -) 



Propodus of external maxillipeds as long as wide. Third pair of 

 walking legs subequal to first and narrower than second pair . 2 



2. Fronto-orbital distance less than one-half width of carapace. Regions 



of carapace not distinguishable, except for a H-shaped figure in 

 the middle. Upper margin of meropodites of middle pair of walking 



legs spinulous Th. orientalis Rathbun ^) 



Fronto-orbital distance equal to one-half width of carapace. Gastric, 



and to a lesser degree the cardiac region, are distinctly defined Th.chuenensis'R^sX\CQ\m^) 



Lambdophallus Alcock. 



1900. LiDiibdopliallus Alcock. Journ. As. Soc. Bengal, v. 69, prt 2, p. 329. 



This genus is founded on the species L. sexpes, which is provided with a deep, trans- 

 verse trench in the first sternal segment of the cf ; it is in ' this trench that the distal part of 

 the rectangularly-bent sexual appendages is lodged. The meropodites of the walking legs are 

 not very much broadened, anterior and posterior margin parallel. The pterygostomian regions, 

 according at least to Alcock's figure °), are provided with some faint oblique striae, resembling 

 those of Hexapiis\ the external maxillipeds, too, are much alike in both genera, but in Lamb- 

 dophalhis the last joint (dactylus) of the palp is not very much produced and as long as the 

 propodus. This species has been dredged in the Bay of Bengal, at a depth of 65 fathoms. 



A second species, L. anfrachis, has in recent years been established by Miss Rathbun, 

 but, as I hope to show (p. 241), it is identical with Hexaptts sexpes. The genus will, on close 

 examination, probably turn out to be only a subgenus of Hexaptts. 



Hexapus de Haan. 

 1835. Hexapus de Haan. Faun. Japon., Crust., p. 35. 



This genus contains but a single species, which, except for his broader walking legs 

 and the elongate dactylus of the palp of the external ma.xillipeds does not materially difier 

 from La>nbdopkalhis. 



1) Stebbing (Ann. S. Afr. Mus., v. 6, 1910, p. 316) throws doubt upon the exactness of Miers' figure of these maxillipeds 

 and calls this figure "very unconvincing", but in this very year Miss Rathbun described in two new species of Thaumastoplax precisely 

 the same kind of maxillipeds, and formerly Ortmann (Zool. Jahrb., Syst., Bd 7, 1894, p. 693) stated that the external maxillipeds of 

 7 ritodynamia are of an identical build. 



2) Ann. Mag. Nat. Hist. (5), v. 8, 1881, p. 261, pi. 14, f. 2. Hab. Goree Island (Senegambia). 



3) Proc. Biol. Soc. Washington, v. 22, 1909, p. 113; K. Dansk. Vid. Selsk. Skr., 7. Raekke, Afd. 5, n" 4, 1910, p. 346, 

 textfig. 33, pi. 2, f. I. Hab. Gulf of Siam. 



4) Proc. Biol. Soc. Washington, v. 22, 1909, p. 113; K. Dansk. Vid. Selsk. Skr., 7. Raekke, Afd. 5, n" 4, 1910, p. 347, 

 textfigs. 34 — 35. Hab. Gulf of Siam. 



5) III. Zool. "Investigator", Crust, prt 10, 1903, pi. 62, f. la. 



91 



