Land Crustacea. 163 



LAND CEUSTACEA. 



By C. W. AxDREws, B.Sc, F.G.S. 



The land Crustacea are a very important factor in the fauna of 

 the island. They seem to act as the chief scavengers, destroying 

 hoth animal and vegetable refuse, while the little red crab 

 {Gecarcmus lagostomm) to some extent takes the place of earth- 

 worms, in loosening the surface soil and incorporating with it the 

 ■decaying vegetable matter. 



I am indebted to Professor Jejffrey Bell and Mr. R. I. Pocock 

 for the determination of the species noticed below. 



Family GECARCIXID^. 

 1. Gecarcinus lagostomus, M -Edw. 



■Gecarcinus lagostoma, M.-Edw., Hist. nat. Crust., vol. ii (1837), p. 27. 

 Sylceocarcinns natalis, Pocock, P.Z.S., p. 531, 1888. 



In his account of the Crustacea of Christmas Island collected 

 hy Mr. J. J. Lister, Mr. E.. I. Pocoek described as new a small 

 crab, to which he gave the name SylcBocarcinus natalis. At the 

 same time he pointed out that the genera Sylceocarciniis of 

 Wood-Mason and Lhmiocarcinus of De Man are probably identical, 

 iind suggested that the differences between them depend on age. 



In the present collection a number of large bright-red crabs, 

 here referred to Gecarcinus lagostomus, are undoubtedly the adult 

 of Sylceocarciniis natalis. 



This is the commonest of the land-crabs inhabiting the island, 

 and is found in great numbers everywhere, even on the higher 

 hiills and the more central portion of the plateau. In many places 

 the soil is honeycombed by its burrows, into which it rapidly 

 retreats when alarmed. These crabs seem to feed mainly on dead 

 leaves, which they carry in one claw, held high over the back, 

 and drag down into the burrows. Prom their enormous numbers 

 they must play a great part in the destruction of decaying vegetable 

 matter and its incorporation into the soil. 



Once a year, during the rainy season, they descend to the sea 

 to deposit their eggs, and during this migration hundreds may be 

 seen on every path down steep slopes, and many descend the 

 clifE-face itself. They remain on the beach for a week or two, 

 and deposit their eggs among stones in shallow water inside the 

 reef. Afterwards they gradually make their way back to their 

 accustomed homes. In the year of my visit this migration occurred 

 in January. 



