128 



Plagusia Latreille. 



1806. Plagusia (part.) Latreille. Gen. Crust. et Insect., t. 1, p. 33 



Alcock s ) states, that in Plagusia the exognath of the external maxillipeds is destitute of 

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

 Borradaile state the occurrence of a flagellum in P. capensis. 



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

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

 hiding in crannies when pursued. They also resemble Varuna 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 3 ). 

 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 fossae with inner 



margins granulate. Chelipeds of <-? very short, outer surface 



of palm smooth, not costate, upper border granulate P. glabra Dana 4 ) 



Carapace always with more or less distinct squamiform tubercles. 

 Chelipeds of ef longer, outer surface of palm longitudinally 

 costate 3 



3. Three teeth behind external orbital angle P . depressa (Fabricius) 5 ) 



Two teeth behind external orbital angle. Carapace wholly covered 



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



1) Kingsley (Proc. Ac Nat. Sc. Philadelphia, 18S0, p. 224, footnote) rightly remarked, that in the dismemberment of Latreille's 

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

 is now generally considered to be identical with Perenon planissimum (Herbst). 



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



3) Rep. Pearl Oyster Fish. Ceylon, pit 5, 1906, p. 429 — 430. 



4) Proc. Ac. Nat. Sc. Philadelphia, 1S51, 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; Miers, Ann. Mag. Nat. Hist. (5) v. 1, 1878, p. 152; Haswell, Cat. Austral. Crust., 18S2, p. ui. 

 Hab. New South Wales. 



5) The typical P. depressa, with squamiform tubercles on the carapace and the lobes(coxal processes) above the bases of the middle 

 pairs 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 tuberculata Lamarck 



Posterior coxal process of 2 n ' and 3' walking legs dentate depressa Fabricius 



Carapace tubercles more depressed — those on gastric region obsolescent. Posterior coxal process of 2°'' and 3' 1 



walking legs entire immaculata Lamarck 



Laurie, however, points out that there must be a tendency of merging one into another among the subspecies. The P. sauamosa 

 ol IIikb-1 is, according to LAURIE, to be discarded, as there is an essential discrepancy, as regards the shape of the coxal processes, 

 between text and figure. 



iiuie of this most common species, up to 1900 at least, is gathered by ALCOCK, Journ. As. Soc. Bengal, v. 69, pit 2, p. 437. 



128 



