Carcinulogical Fauna of India. 431 



oidal gap, in which the mandibles are exposed : a broad oblique groove, 

 bounded internally by a line of hairs, i-uns from a point behind the 

 antero-external angle of the ischium to the anterior edge of the merus : 

 the merus is truncated, and the foliaceous propodite articulates near its 

 antero-external angle. 



The chelipeds differ very markedly in the sexes : in the female 

 they are shorter and slenderer than the legs, but in the male they are 

 longer and mucli m.ore massive than the legs. In the male there is 

 always a short oblique horny crest, either on or close to and pai'allel 

 with, the inner boi'der of the arm, as in many species of Macrophthalnuis : 

 it probably, as Dr. de Man suggests, is scraped against the lower border 

 of the orbit to produce a musical sound. 



Legs slender, the first and last pairs much shorter than the 2nd 

 and 3rd pairs — the 3rd pair the longest. 



The abdomen in the male does not quite cover the sternum between 

 the bases of the last pair of legs : it may have all 7 segments distinct, 

 or, rarely, the 3rd 4th and 5th segments may be fused together : in the 

 female all 7 segments are separate and the 7th is small and deeply 

 impacted in the 6th, as in Sesarma. 



Distribution ; Estuaries and mudflats of the Oriental littoral. 



The species of Metaplax have many points of resemblance with the 

 Ocypodoid genus Macrophthahnus, and this is all the more likely to lead 

 to confusion as the two genera share the same habitat and have the 

 same manner of life ; but there is no doubt of the true position of 

 Metaplax among the Sesarminsd. 



Key to the Indian species of Metaplax. 



I. Anterior border of carpi and propodifces of legs spiny : 



chelipeds iu the male 3 times the length of the carapace M. crenulata. 



II. Anterior border of carpopodites and propodites of legs 

 smooth : male chelipeds less thaa 3 times the length of the 

 carapace : — 



1. Dactylus of chelae of male without any prominent 



lobe on its dentary edge : chelipeds of male equal : — 



i. 3rd 4th and 5th abdominal segments fused 



together in the male i -Af. iiidica. 



ii. All the abdominal segments separate : — 



a. Length of the carapace about three- 

 fourths the breadth : orbital portion of 



* lower border of orbit with 4 or 5 teeth... M. dentipes- 



b. Length of the carapace less than three- 

 fourths the breadth : orbital portion of 



lower border of orbit with 9 or 10 teeth... M. distincta. 



773 



