155 



and ciliata. The first species, however, certainly belongs to EiLcrate de Haan; longipes is very 

 obscurely known, but according to Stimpson's posthumous treatise ^) the front is "deflexed and 

 emarginate at the middle" and with a supra-marginal line of long hairs, which suggests an 

 affinity to LitocJicira Kinahan ; scitlpta is according to Stimpson's figure ") too much sculptured 

 to belong to Pihiinnoplax and the front is likewise deflexed^); finally ciliata is doubtless a 

 species of Litocheira. 



The name should, then, become a synonym, partly of Eiicratc, partly of LitocJieira, 

 but MiERS afterwards included into Pilumnoplax two species, which certainly warrant the 

 constituting of a new genus and, though strictly speaking the name given by Stimpson is not 

 admissible, I have retained it here. We must in this case adhere to Alcock's definition *) of 

 the genus, and particularly exclude from it those species with the front turned strongly down 

 and bilobed; in genuine Pihivinoplax the front is, on the contrary, feebly deflexed, 

 in a line with the general longitudinal curve of the carapace, overhanging 

 the antennulae, and with the anterior margin perfectly straight and usually 

 entire; the carapace is flattened from side to side and hairless; the ambulatory legs are slender. 



The species of the genus thus restricted are all inhabitants, as far as is known, of the 

 deeper parts of the ocean bottom, save P. vestita (de Haan), which seems to live in shallow 

 water. This species deviates also in its outer aspect from the other species, for the carapace, 

 the legs and especially the chelae are very hairy, the front does not overhang the antennules, 

 and the legs are stout and short; yet, following Miers and Ortm.vnn, I have let it retain its 

 place in the present genus. On the other hand I have serious doubts about the true systematic 

 place of P. acanthomertis Rathbun °), found at only 30 fathoms near the Amirante Islands in 

 the Western Indian Ocean. This species has the front nearly half as broad as the carapace, 

 with the anterior edge sinuous, emarginated in the middle and near each lateral angle, the 

 chelipeds and ambulatory legs are profusely spinj-, stout and bulk}'. 



I thus admit only the following species, one of which has been brought home by the "Siboga" : 



P. vestita (de Haan) 

 P . heterochcir (Studer) 

 P. abyssicola Miers 

 P. g/aderrinia Ortmann 

 P. americana Rathbun 

 P. cooki Rathbun. 



Key to the species ; 

 I . Carapace much hairy, with two widely separated, little prominent 

 teeth behind each external orbital angle. Chelae with a lona; 

 fur on proximal and upper part of outer surface. Ambulatory 



1) Smithson. Inst., Miscell. Coll., v. 49, 1907, p. 91. 



2) Ibid., p. 91, pi. II, f. 3. 



3) I shall refer to this species later on, as the "Siboga" caught a species nearly related to it. 



4) "Investigator" Deep Sea Brachyura, 1899, p. 74; Journ. As. Soc. Bengal, v. 6g, pit 2, 1900, p. 311. 



5) Transact. Linn. Soc. London (2), v. 14, 1911, p. 237, pi. 18, f. 3. 



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