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Plagusia Latreille. 

 1806. Plagusia (part.) Latreille. Gen. Crust, et Insect., t. i, p. 33 '). 



.Alcock-) States, that in Plagusia the exognath of the e.Kternal maxillipeds is destitute of 

 a flagellum, but already de Haan has figured one in P. dentipes, and both Stebbing and 

 BoRRAD.\TLE State the occurrence of a flagelhim in P. capensis. 



Alcock also remarks, that the habits of this genus (and of Percnon) "to a certain 

 e.vtent resemble (those of) the Grapsi, dodging about rocks that are awash at high tide, and 

 hiding in crannies when pursued. They also resemble Variina in being able to make themselves 

 at home on drift timber in the open sea. This will account for the very wide range of some 

 of the species'". Indeed, both genera contain an almost cosmopolitical species, occurring every- 

 where on tropical coasts; in the genus Plagusia this widely-spread species is separable into 

 several subspecies, as has been clearly traced out by Laurie^). 

 Key to the species : 



1. Meropodites of the ambulatory legs with one subterminal tooth 



on its upper border 2 



Meropodites of the ambulatory legs with a series of teeth on its 

 upper margin. Carapace almost entirely destitute of tubercles 4 



2. Carapace smooth, not squamose. Interantennular fo.ssae with inner 



margins granulate. Chelipeds of cf very short, outer surface 



of palm smooth, not costate, upper border granulate . . . P. glabra Dana ^) 

 Carapace always with more or less distinct squamiform tubercles. 

 Chelipeds of cf longer, outer surface of palm longitudinally 

 costate 3 



3. Three teeth behind external orbital angle P. dcpressa (Fabricius) '") 



Two teeth behind external orbital angle. Carapace wholly covered 



with large, squamiform tubercles. Palm of chela at outer surface 



i) KiNC.si.icy (Pioc. Ac Nat. Sc. I'hiladelphia, 1880, p. 224, footnote) lightly remarked, that in the dismemberment of Latreille's 

 genus the name Plagusia should have been given to Percnon, for the first species mentioned by Latreille is Plagusia clavimana, which 

 is now generally considered to be identical with Percnon planissituum (Herbst). 



2) Journ. As. Soc. Bengal, v. 69, prt 2, 1900, p. 437. 



3) Rep. I'earl Oyster Fish. Ceylon, prt 5, 1906, p. 429 — 430. 



4) Proc. Ac. Nat. Sc. Philadelphia, 1851, p. 252; U.S. Expl. Exp., Crust., 1852, p. 371, pi. 23, f. 10; H. Milne-Edwards, 

 Ann. Sc. Nat. (3) t. 20, 1853, p. 179; MrERS, Ann. Mag. Nat. Hist. (5) v. I, 1878, p. 152; Haswell, Cat. AustraL Crust., 1882, p. lii. 

 Hab. New South W.iles. 



5) Ihe typical P. dcpressa, with sriuamiform tubercles on the carapace and the lobes (coxal processes) above the bases of the middle 

 p.iirs of walking legs dentate, is chiefly Atlantic, and even occurs in the Mediterranean. The subspecies are thus divided by Laurie (1. c.) : 

 Carapace covered with numerous — often more or less squamiform — tubercles, each bordered by a fringe of short 



stiff hairs: 



Posterior coxal process of 2"'' and 3' walking legs entire tuhercuhUa l^axaaxcV 



Posterior coxal process of 2"' and 3' walking legs dentate . ieprcssa Fabricius 



Carapace tubercles more depressed — those on gastric region obsolescent. Posterior coxal process of 2'"' and 3' 



walking legs entire immaculala Lamarck 



Laurie, however, points out tliat there must be a tendency of merging one into another among th» subspecies. '^\\t P. squamosa 

 of Meriist is, according to Laurik, to be discarded, as there is an essential discrepancy, as regards the shape of the coxal processes, 

 between tex-t and figure. 



The literature of this most common species, up to 1900 at least, is gathered by Alcock, Journ. As. Soc. Bengal, v. 69, prt 2, p. 437. 



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