ii6 



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

 (in the d) 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 He/ice and ChasmagnatJms, 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 neighbouring 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 [Ai. 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: 



1. Carpo- and propodite of the walking legs spinulose 



along the anterior margin ]\I. crciuilata (Gerstaecker) ^) 



Carpo- and propodite of the walking legs not spinulose 

 along the anterior margin , . 2 



2. Number of lobules or teeth of the infra-orbital ridge 



of the cf 7—9 3 



Number of lobules of the inlra-orbital ridge numerous, 

 more than 20 4 



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



orbital part. Abdomen of cT consisting of 7 free 



segments M. longipes Stimpson ") 



Infra-orbital ridge beginning near the epistome with 

 4 — 5 very small teeth, followed 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''^ — 5''' segment 

 of abdomen of cT partly fused Al. indica H. Milne-Edwards^) 



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

 Lobules of infra-orbital ridge amounting to 40 — 60 



(about 35 in 9) 6 



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



rapidly decreasing in size laterally and backward. 



1) Khaconohis t-/-<'««/ai'Kj Gerstaecker, Arch. Nauirgesch., Jahrg. 21, 1856, p. 142, pi. 5, f. 5: Metaflax c. de Man, Journ. Linn. 

 Soc. London, v. 22, 1888, p. 156; Zool. Jahrb., Syst., Bd 4, 1889, p. 439: M. cremilata Alcock, Journ. As. Soc. 'Bengal, v. 69, prt 2, 

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



2) Proc. Ac. Nat. Sc. Philadelphia, 1858, p. 97; Koei.bel, Wiss. Erg. Reise Szechenyi in Ost-Asien 1S77— 18S0, Bd 2, 189S, 

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



3) Ana. Sc. Nat. (3) t. iS, 1852, p. i6l: Arch. Mus. Paris, t. 7, 1855, pi. 11, f. 2; M. m.ika .'Ucock, Journ. As. Soc. Bengal, 

 V. 69, prt 2, 1900, p. 432. Hab. Karachi (British India). 



116 



