RETROPLUMIDAE. 



This family was instituted by Gill ^) to receive the genus Arc/iaeoplax, established by 

 Alcock and Anderson ") in the previous year for an aberrant deep sea Crab. Becoming aware 

 that this name Archaeoplax was praeoccupied, the latter authors changed the name into Pte- 

 iioplax '), but already Gill had changed the generic name into Retrophima, and accordingly 

 the term Retroplumidae has priority above Ptenoplacidae. Nevertheless, such competent authors 

 as BoRRADAiLE *) retain Alcock's nomenclature, and so does Mac Gilchrist '"). Only Doflein *), 

 in describing a new species, has followed Gill. 



As to the generic affinities, ample information has been given by Alcock (1. c. 1 899) 

 and BoRRADAiLE. Only a single genus is known, the species of which inhabit the deeper parts 

 of the sublittoral zone and may be called almost abyssal. 



Retropluma Gill. 



Literature: Doflein I.e. Alcock has excellently characterized this genus (I.e. 1899). 

 Two species have been described, but the "Siboga" Expedition has yielded a third one. 



1. Side margins of carapace with only one tooth (or rather angulation) 



behind ext. orb. angle. Rostrum expanded and bilobed at tip. 



Superior orbital border with a small projection in the middle . . R. notopus (Alcock) 

 Side margins of carapace with two teeth (or angulations) behind ext. 

 orbital angle. Rostrum regularly tapering to tip, not expanded or 

 bilobed. Superior orbital border either without any prominence or 

 with a strong tooth 2 



2. Sides of carapace strongly toothed. Supra-orbital tooth spiniform, 



directed forward and half as long as rostrum. Transverse sutures 



1) Americ. Naturalist, v. 28, 1894, p. 1043. 



2) Journ. As. Soc. Bengal, v. 63, prt 2, 1895, p. 180. 



3) 111. Zool. "Investigator", Crust., 1895, pi. 15. Cf. Alcock, Account Deep-Sea Brachyura "Investigator", Calcutta, 1899, p. 78. 



4) Ann. Mag. Nat. Hist. (7) v. 19, 1907, p. 479. 



5) A'nn. Mag. Nat. Hist. (7) v. 15, 1905, p. 266. 



6) Wiss. Erg. ''Valdivia"-Exp. Bd 6 (Brachyura), 1904, p. 131. 



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