i i6 



The species are in the possession of a "musical ridge" on the arm of the cheliped 

 1 i ti the cf) and of a peculiarly-transformed infra-orbital margin, the mode of crenulation of 

 which is of great systematic value; these characters, though not so constantly observed, are 

 also shared by the genera Helice and Chasmagnathus, both established by de Haan, to which 

 Metaplax is closely related. 



The majority of the species inhabit mud-flats near the mouths of rivers in British India 

 and the ncighbouring islands, where they seem to be most numerous in individuals. One species 

 inhabits China (Hongkong); it is aberrant by having the anterior margin of the meropodites 

 of the walking legs not spinulose, but at most granulate. Towards the Indo-Malayan Archipelago 

 only one species extends [M. elegans de Man), that has been observed at the coasts of Atjeh, 

 of Borneo (Pontianak and Samarinda) and at Macassar. The "Siboga" collection did not contain 

 a single representative of the genus. 



Key to the species : 

 i. Carpo- and propodite of the walking legs spinulose 



along the anterior margin M. crcnulata (Gerstaecker) J ) 



Carpo- and propodite of the walking legs not spinulose 

 , along the anterior margin . . 2 



Number of lobules or teeth of the infra-orbital ridee 



o 



of the (f 7 — 9 



Xumber of lobules of the infra-orbital ridgre numerous, 

 more than 20 4 



3. Infra-orbital ridge with three large lobules in the 



orbital part. Abdomen of cf consisting of 7 free 



segments M. lojigipes Stimpson = ) 



Infra-orbital ridge beginning near the epistome with 

 4 — 5 very small teeth, foliowed by two larger, 

 rounded lobules, that are separated by a large 

 interspace from three very small tubercles in the 

 lateral or hind part of the ridge. 3 th — 5 tb segment 

 of abdomen of cf partly fused M. indica H. Milne-Edwards 3 ) 



4. Lobules of infra-orbital ridge amounting to 25 — 30 5 

 Lobules of infra-orbital ridge amounting to 40 — 60 



(about 35 in Q) 6 



5. Lobules of orbital portion very large (6 in the adult cf ), 



rapidly decreasing in size laterally and backward. 



ij Rhaconotus crénulalus Gerstaecker, Arch. Naturgesch., Jahrg. 21, 1856, p. 142, pi. 5, f. 5: Metaplax c. de Man, Journ. Linn. 

 1 ondon, v. 22, 1888, p. 156; Zool. Jahrb., Syst., Bd 4, 18S9, p. 439; M. crcnulata Alcock, Journ. As. Soc. Bengal, v. 69, pit 2, 

 1900, p. 435. Hab. Bay of Bengal. 



2) Proc. Ac. Nat. Sc. Philadelphia, 185S, p. 97; Koet.bel, Wiss. Erg. Reise Széchenyi in Ost-Asien 1S77 — 18S0, Bd 2, 1S9S, 

 p. 569, pi. 1 f. 1 — 4; Stimpson, Smithson. Inst., . Miscéll. Coll., v. 49, 1907, p. 99. Hab. Hongkong. 



3) Ann. Sc. Nat. (3) t. 18, 1852, p. 161; Arch. Mus. Paris, t. 7, 1S55, pi. 11, f. 2; Af. indica Alcock, Journ. As. Soc. Bengal, 

 v. 69, pit 2, 1900, p. 432. Hab. Karachi (British India). 



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