2o6 Memoirs of the Indian Museum. [Voi,. V, 



locality a small colony of Dotilla clepsydrodactylus was found. In the same month , in 

 other parts of the outer channel, a few immature specimens of Matuta victor and single 

 examples of Dotilla myctiroides , Sesarma tetragonum, Plagusia depressa tuberculata, 

 Leander styliferus and Leptochela aculeocaudata were obtained. Although special 

 efforts were made, these species were not to be found later in the year when the 

 water was fresh and, from the evidence we are able to offer, it appears that they are 

 merely visitors, either brought by chance into the position in which they were found, 

 or seeking shelter from the breakers on the coast-line in the still waters at the mouth 

 of the lake. They are unable to withstand the great alterations in salinity to which 

 the outer channel is subject and in the flood-season must either retire to the sea 

 or perish. 



There is evidence that the two species of the almost terrestrial genus Coenobita, 

 found in the outer channel, had migrated from the sea-shore, for some of our speci- 

 mens were inhabiting marine shells not found in a living condition in the lake. The 

 great majority of the specimens were very small and no ovigerous females were 

 obtained. We regard these species also as casual visitors. 



The great majority of the casual visitors from the sea are species of wide Indo- 

 pacific distribution. 



Palaemon scabriculus , of which two specimens were obtained in brackish water at 

 the mouth of a small stream running into Rambha Bay, is apparently a casual visitor 

 from fresh water. 1 



Although our knowledge of other bodies of water of low or variable salinity on 

 the Indian coast is still meagre, it is possible to institute some comparison between 

 the Decapod fauna of the Chilka Lake and that of the Gangetic delta and of the 

 backwaters near Madras. 



The following species, permanent inhabitants of the Chilka Lake, are also known 

 from brackish water in the Gangetic delta, to the Crustacea of which the late Mr. 

 J. Wood-Mason and Col. Alcock devoted much attention: — 



Pachygrapsus propinquus . Clibanarius padavensis. 



Varuna litterata. Penaeus carinatus. 



Scylla serrata. Penaeus indicus. 



Neptunus pelagicus. Penaeopsis monoceros. 



Metaplax and Hymenicus , genera which are plentiful in the Gangetic delta, do 

 not occur in the lake. 



A far larger number of species are common to the Chilka Lake and to the back- 

 waters near Madras. Our knowledge of the Decapod fauna of the latter is due to 

 the researches of Dr. J. R. Henderson and to the collections recently made by Dr. 

 Annandale at Ennur : — 



] A Potamonid crab, Paratelphusa (Oziotelphusa) hydrodromus (Herbst), is common in rice-fields, 

 streams and artificial ponds in the surrounding country. Though we have never found it in the lake 

 itself, it may occasionally wander there in the flood-season. 



