3o6 Records of the Indian Museum. [Vol. XVI, 



arrangement of the pellets gives the burrow a very characteristic 

 appearance, enabling it to be distinguished at a glance from that 

 of young Ocypoda and other forms of similar habits. 



The crabs are gregarious and sometimes occur in very large 

 numbers. Beaches occupied by them can occasionally be recognised 

 at a considerable distance by their freshly raked surface. Little 

 is known as to what occurs in these communities at high tide, but 

 as they are very seldom obtained in nets hauled on suitable ground 

 near the shore it is probable that they remain in their burrows. 

 When the tide is out they may often be seen sitting at the mouths 

 of the burrows or in the pathways leading to them, but seldom if 

 ever wander further afield. Each crab or pair of crabs keeps 

 rigidly to its burrow. 



The habits of the Indian species of Dotillopsis seem to be 

 somewhat different from those of the other genera because the mud 

 in which it burrows is too soft to retain a definite impression. It 

 is often impossible to distinguish its holes, though it appears to 

 excavate them in the same way. The dense tomentum on the 

 walking legs in this genus and in certain species of Tympanomerus 

 is probably an adaptation to life on muddy ground. 



Most of the species of Dotilla and Scopimera live on the sea- 

 shore. A few make their way into backwaters, where the water 

 is brackish or of very variable salinity, but the environment in 

 such situations is as a rule unfavourable. The crabs usually fail 

 to reach their normal size, and in species in which there are 

 marked structural differences between the sexes, the males seem 

 unable to attain their full development. 



Most species of Tympanomerus are found in estuaries, often 

 near or even beyond the extreme limit of tidal influence. Both 

 species of Dotillopsis are essentially estuarine, but the Indian form 

 has been found in a small backwater near the open sea as well as a 

 considerable way up the Gangetic delta. No species has been 

 found at any great distance from the coast, but T deschampsi and 

 T. stapletoni are able to live on the banks of large rivers at places 

 wheie the water is always fresh. T. stapletoni is said to have 

 destroyed a dynasty of kings in Eastern Bengal by burrowing 

 through the embankments their people had constructed and so 

 letting brackish water in to the rice-fields. 



In examining the Indian species of Scopimerinae I have met 

 with instances of dimorphic forms in the female as well as in the 

 male sex. In Dotilla intermedia two perfectly distinct types of 

 adult male exist which differ conspicuously in the structure of the 

 first segment of the abdominal sternum and chela and in the form 

 of the copulatory appendage. Scopimera proxima presents still 

 more interesting features, for it exhibits dimorphism of the female — 

 a phenomenon not, I think, hitherto noticed in Decapod Crustacea. 

 The dimorphism in this instance is to be found in the form of the 

 abdomen and is very peculiar in that the scarcer and more aberrant 

 form of female has characters approximating closeh^ to those of 

 the male. The remarkable point is that in this form the sides of 



